REESE  LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


5VO 


A  MANUAL 


OF 


PRACTICAL  ASSAYING. 


BY 

H.  VAN  F.  FURMAN,  E.M., 

Late  Professor  of  Mining  and  Metallurgy ,  Colorado  State  School  of  Mines:  Late  Chemist 
and  Assayer  of  the  Germania  Lead  Works,  Salt  Lake  City,  Utah  ;  Late  Chemist  and 
Assistant  Metallurgist  of  the  Rio  Grande  Smelting  Works,  Socorro,  M.N.: 
Late  Chemist  of  the  Globe  Smelting"  and  A'e 'fining  Co,,  Denver,  Colo,: 
Late  Chief  Assay  tr  of  the  United  States  Mint,  Denver,  Colo.: 
Late  Superintendent  and  Metallurgist  of  the  Compania 
Minera  de  Penoles,  Mapimi,  Mexico  ;  Member 
of  the.   American  iKstitute  of  Mining 
Engineers  ;  Member  of  the  Colo- 
rado Scientific  Society  ;  etc. 


FIFTH  EDITION,  REVISED  AND  ENLARGED* 
FIRST    THOUSAND. 


NEW   YORK : 

JOHN    WILEY   &   SONS. 

LONDON:    CHAPMAN   &    HALL,    LIMITED. 

1899. 


Copyright,  1893, 

BY 
H.  VAN  F.  FURMAN. 


ROBERT   DRUMMOND,    BLECTROTYPKR   AND    PRINTER,    NEW     YORK. 


PREFACE   TO   THE    FIFTH    EDITION. 


WHILE  there  have  been  no  very  marked  changes  in  this 
edition,  yet  the  work  has  been  carefully  examined,  some 
typographical  errors  have  been  corrected,  and  some  modifica- 
tions have  been  made  in  certain  parts,  due  to  the  description 
of  new  methods.  There  have  also  been  added  Appendices 
F  and  G. 

At  the  present  time  the  concentration  of  gold  ores  is  a 
subject  of  great  importance  in  the  United  States  and  else- 
where, and  as  the  assayer  may  frequently  be  called  upon  to 
make  laboratory  tests  Appendix  F  has  been  incorporated. 
It  contains  the  mechanical  assay  of  gold  and  silver  ores  by 
a  combination  of  the  processes  of  amalgamation  and  concen- 
tration; these  are  described  at  some  length  and  are  illus- 
trated by  diagrams,  with  certain  necessary  tables,  and  the 
latest  available  data  have  been  added. 

Appendix  G  contains  the  calculation  of  copper-matte 
blast-furnace  charges;  also  valuable  material,  derived  from 
actual  experience.  This  matter  was  originally  published  by 
the  author  in  the  School  of  Mines  Quarterly  of  Columbia 
University.  The  article  is  now  out  of  print  and  has  been 
incorporated  in  "  Practical  Assaying"  because  the  author 
has  received  numerous  requests  from  chemists  and  metallur- 
gists for  reprints. 

It  is  believed  that  the  work  is  now  quite  abreast  of  the 
latest  investigations  and  discoveries  in  the  subject  treated. 

H.  VAN  F.  FURMAN. 

309  BOSTON  BUILDING,  DENVER,  COLO., 
November,   1899. 

iii 


82929 


PREFACE  TO  THE  FOURTH   EDITION. 


IN  presenting  the  present  edition  of  "  Practical  Assaying  " 
to  the  public  it  is  but  proper  to  state  that  the  work  has  been 
revised  and  a  number  of  the  chapters  have  been  entirely  re- 
written. The  most  important  changes  have  been  made  in  the 
chapters  on  the  determination  of  lead,  copper,  bismuth,  iron, 
zinc,  and  gold  and  silver  in  ores  and  copper  products,  the  assay 
of  gold  bullion  and  the  assay  of  platinum  alloys. 

The  matter  contained  in  the  Appendix  is  new  to  the  pres- 
ent edition. 

In  conclusion,  I  wish  to  acknowledge  my  indebtedness  to 
numerous  friends  for  their  kind  suggestions  and  criticisms  and 
particularly  to  Mr.  William  Orr,  of  the  Gold  and  Silver  Ex- 
traction Co.  of  America,  and  Mr.  Philip  Argall,  of  the  Metal- 
lic Extraction  Co.,  of  Florence,  Colo.,  for  much  of  the  matter 
contained  in  Appendix  D. 

H.  VAN  F.  FURMAN. 

DENVER,  COLO.,  March,  1896, 

iv 


PREFACE. 


SOME  three  years  ago  there  was  published  in  The  Mining 
Industry  of  Denver,  by  the  author  of  the  present  volume,  a 
series  of  articles  entitled  "  Notes  on  Technical  Chemical 
Analyses."  The  articles  were  favorably  received  by  the  tech- 
nical public,  and  in  compliance  with  numerous  requests  their 
republication  in  the  present  book  form  was  undertaken* 

It  is,  however,  proper  to  state  that  the  original  articles 
have  been  rewritten  and  much  new  matter  has  been  added, 
embracing  all  the  new  technical  methods  which  have  been  in- 
troduced and  proved  trustworthy  since  the  publication  of  the 
series  referred  to,  as  well  as  many  determinations  not  described 
there. 

Greatest  prominence  has  been  given  to  the  rapid  methods 
in  vogue  in  the  technical  laboratories  of  the  United  States, 
supplemented  by  a  detailed  description  of  some  of  the  longer 
and  more  exact  ones. 

Although  the  plan  of  the  work  presupposes  a  knowledge  of 
the  general  principles  of  chemistry,  the  endeavor  has  been  to 
present  the  methods  in  a  form  that  those  having  but  a  more 
limited  experience  in  analytical  chemistry  could  successfully 
perform  the  operations. 

Chapter  III  of  Part  IV,  while  not  strictly  within  the  scope 
of  a  work  of  the  present  nature,  was  included  to  illustrate  the 
practical  application  of  the  principles  of  stoichiometry  and 
chemistry  to  metallurgy. 

Reference  has  been  made  by  footnotes  to  the  original  sources 


vi  PREFACE. 

of  information.  Where,  inadvertently,  omissions  have  occurred 
and  due  credit  has  not  been  so  given,  the  author  would  esteem 
it  a  favor  to  have  his  attention  called  to  the  neglect.  He 
would  also  be  pleased  to  receive  criticisms  on  the  work,  so  that 
he  may  be  able  to  take  advantage  of  them  should  a  future 
edition  be  called  for. 

In  conclusion  the  author  begs  to  add  that  should  this  little 
volume  fill  even  partially  the  wants  of  technical  chemists  and 
meet  with  their  approval,  he  will  feel  amply  repaid  for  the 
labor  involved  in  the  compilation  and  publication  of  the 
methods  described. 

H.  VAN  F.  FURMAN. 

DENVER,  COLO.,  September  30,  1893. 


TABLE  OF  CONTENTS. 


PART  I. 

INTRODUCTORY. 
CHAPTER  PAGS 

I.   Introduction .  x 

II,  Sampling 5 

III.  Preliminary  Examination 21 

IV.  Apparatus  and  Operations 49 

V.  Reagents 66 


PART  II. 

DETERMINATIONS. 

I.  Silica 77 

II.  Sulphur 88 

III.  Phosphorus 100 

IV.  Carbon 106 

V.  Carbonic  Acid lib 

VI.  Water 119 

VII.  Gold  and  Silver 122 

VIII.  Mercury 133 

IX.  Lead 136 

X.  Arsenic   144 

XI.  Antimony 147 

XII.  Tin 151 

XIII.  Copper 154 

XIV.  Bismuth : 163 

XV.  Cadmium    166 

XVI.   Iron.. 168 

XVII.  Aluminium 181 

XVIII.  Chromium i&8 

XIX.  Titanium 190 

XX.  Manganese *94 

vii 


VJii  CONTENTS. 

PAGE" 
CHAPTER 

XXI.  Zinc 205 

XXII.  Nickel  and  Cobalt 211 

XXIII.  Calcium 215 

XXIV.  Magnesium 220 

XXV.  Barium 224 

XXVI.   Sodium  and  Potassium 227 

PART  III. 

SPECIAL   ASSAYS   AND   ANALYSES. 

I.  Assay  of  Base  Bullion 232 

II.  Assay  of  Silver  Bullion : 236 

III.  Assay  of  Gold  Bullion 246 

IV.  Special  Method  for  the  Assay  of  Copper  Matte,  etc 250 

V.  Assay  of  Silver  Sulphides  252 

VI.  Chlorination-assay  of  Silver  Ores 254. 

VII.  Chlorination-assay  of  Gold  Ores 256 

VIII.   Assay  of  Gold  and  Silver  Ores  containing  Metallic  Scales 258 

IX.  Amalgamation-assay .  . 260 

X.  Analysis  of  Coal  and  Coke 263 

XI.  Analysis  of  Gases 269 

XIL  Analysis  of  Water. 274 

XIII.  Acidimetryand  Alkalimetry 282 

XIV.  Chlorimetry 289 

XV.  Analysis  of  White  Lead 291 

XVI.  Specific-gravity  Determinations ....   293 

XVII.  Analysis  of  Commercial  Aluminium 298 

XVIII.  Analysis  of  Natural  Phosphates 300 

XIX.  Analysis  of  Copper  and  Lead  Slags „ . . .   307 

XX.   Assay  of  Gold-Alloys  containing  Silver  and  Platinum 31 1<* 

PART  IV. 

CALCULATIONS. 

I.  Writing  of  Chemical  Equations 312 

II.  Stoichiometry 32 1 

III.  The  Calculation  of  Lead  Blast-furnace  Charges 337 

TABLES 353 

APPENDIX  A.  Melting  and  Refining  Gold  Bullion 371 

B.   The  Preparation  of  Pure  Gold  and  Silver 382 

"          C.  Losses  of  Gold  and  Silver  in  the  Fire-assay 386 

"  D.  Laboratory  Tests  in  Connection  with  the  Extraction  of  Gold 

by  the  Cyanide  Process 401 

"  E.  The  Analysis  of  Refined  Copper 412 

"  F.  The  Mechanical  Assay  of  Gold  and  Silver  Ores   417 

"          G.  The  Calculation  of  Copper-matte   Blasi-furnace  Charges. . .  .   428 
INDEX  443 


A  MANUAL  OF  PRACTICAL  ASSAYING. 


CHAPTER  I. 
INTRODUCTION. 

ASSAYING  as  practised  in  the  United  States,  and  particu- 
larly as  practised  in  the  Far  West,  may  be  said  to  include  all 
those  operations  of  analytical  chemistry  which  have  for  their 
object  the  determination  of  the  value  of  ores  and  metallur- 
gical products.  Results  are  obtained  by  the  following  three 
methods:  1st.  Fire-assay  (dry  method);  2d.  Gravimetric 
analysis  in  the  wet  way ;  3d.  Volumetric  analysis  in  the  wet 
way.  In  this  classification  the  colorimetric  methods  are 
included  in  the  division  of  volumetric  analysis. 

Fire-assay  determinations  involve  the  separation  of  the 
metal  sought  from  the  other  constituents  of  the  ore  by  the  aid 
of  heat  and  suitable  fluxes,  and  its  estimation  by  weighing  in  a 
state  of  purity.  For  example,  if  the  object  is  the  determina- 
tion of  lead  in  an  ore,  the  ore  is  mixed  in  a  crucible  with  suit- 
able fluxes  and  fused.  The  lead  is  reduced  to  the  metallic 
state,  in  which  condition  it  is  readily  detached  from  the  slag  for 
weighing. 

Gravimetric  determinations  involve  the  separation  of  the 
substance  from  the  other  constituents  of  the  ore,  and  its  esti- 
mation by  weighing  either  the  substance  itself  in  a  state  of 
purity  or  as  a  constituent  of  a  chemical  compound  whose  com- 


fcA  PRACTICAL   ASSA  YING. 

position  is  accurately  known.  For  example,  if  the  object  is 
the  determination  of  lime  in  a  mineral,  the  latter  may  be 
treated  in  such  a  manner  that  the  ultimate  product  of  such 
treatment  is  pure  lime,  which  can  be  weighed  direct ;  or  the 
treatment  may  be  such  that  the  product  is  calcium  sulphate, 
whose  weight  may  be  determined,  and  as  this  salt  is  of  invari 
ble  composition  the  contained  lime  can  readily  be  calculated. 

Volumetric  determinations  are  those  which  involve  the 
separation  of  the  substance  to  be  determined  from  all  inter- 
fering constituents  of  the  ore,  and  the  final  measuring  of  the 
quantity  of  a  solution  necessary  to  complete  a  certain  re- 
action ;  or,  as  in  the  case  of  colorimetric  determinations,  by 
measuring  the  color  imparted  to  a  definite  quantity  of  the 
liquid  by  the  constituent  sought  in  comparison  with  the  color 
imparted  to  the  same  quantity  of  water,  or  other  suitable  fluid, 
by  a  known  quantity  of  the  constituent  sought.  For  example, 
if  the  object  is  the  determination  of  iron  in  an  iron  ore,  as  the 
iron  is  capable  of  reduction  from  the  ferric  to  the  ferrous  state, 
and  of  subsequent  oxidation  to  the  ferric  state  by  the  addition 
of  a  suitable  oxidizing  reagent,  if  the  amount  of  oxidizing  agent 
necessary  to  just  convert  the  iron  to  the  ferric  state  is  known, 
the  amount  of  iron  in  the  substance  can  be  readily  calculated. 

In  fire-assaying  generally  but  one  constituent  of  the  ore  is 
determined  in  each  assay, — except  in  the  case  of  gold  and  silver 
determinations,  where  frequently  both  the  gold  and  silver  are 
determined  in  the  same  portion. 

In  gravimetric  analysis  frequently  several  or  all  of  the  con- 
stituents of  the  substance  are  determined  in  the  one  portion 
taken  for  analysis. 

In  volumetric  work  generally  a  separate  portion  is  taken  for 
each  determination. 

The  following  hints  may  be  of  benefit  to  the  young  and  in- 
experienced chemist: 

Cleanliness  is  absolutely  essential  to  good  work. 

The  work  should  be  systematically  arranged  and  carried 
out.  The  secret  of  accomplishing  a  large  amount  of  work  and 
avoiding  errors  depends  largely  upon  being  systematic.  The 


IN  TR  OD  UC  TION.  3 

apparatus  and  reagents  should  be  adapted  to  the  work,  and 
should  be  systematically  arranged.  A  system  of  labelling  and 
keeping  track  of  each  sample  through  all  stages  of  the  analysis 
should  be  adopted.  By  this  means  mixing  of  samples  will 
be  impossible,  and  a  glance  will  show  at  any  time  just  how 
far  the  analysis  has  proceeded.  A  good  system  of  labelling 
is  to  prepare  some  pieces  of  heavy  paper  about  one  and 
a  half  inches  square.  As  the  substance  is  weighed  out  mark 
the  number  or  name  of  lot,.the  elements  to  be  determined,  and 
weight  taken  on  one  of  these  squares  of  paper,  and  carry  the 
same  along  through  the  course  of  the  analysis  with  the  casse- 
role, beaker,  etc.,  containing  the  sample,  making  simple  marks 
on  the  paper  from  time  to  time,  as  necessary,  to  show  the  stage 
of  the  analysis. 

Where  much  work  is  to  be  done  do  not  attempt  to  carry  a 
few  determinations  through  the  different  stages  of  the  analysis 
to  a  finish  at  once,  but  start  a  number  of  determinations  and 
carry  them  along  through  the  different  stages  in  series,  as  many 
as  convenient  at  a  time. ' 

Use  definite  weights  in  weighing  out  a  substance  for  analy- 
sis, as  0.5  or  i.o  gm. 

Do  not  make  up  the  reagents  indiscriminately,  but  always 
try  and  have  them  of  a  definite  strength.  In  this  way  the  use 
of  excessive  quantities  of  reagents  will  be  avoided.  The  use 
of  excessive  quantities  of  reagents  not  only  unnecessarily 
prolongs  the  operations,  but  frequently  spoils  the  results,  or 
renders  it  impossible  to  obtain  results.  This  applies  to  water 
as  well  as  other  reagents.  The  smallest  quantity  of  a  reagent 
which  will  thoroughly  do  the  work  required  of  it  should  be 
used. 

In  making  up  standard  solutions  for  volumetric  analysis 
care  should  be  exercised  to  have  them  of  the  proper  strength ; 
they  should  be  thoroughly  mixed  and  accurately  standardized. 
It  is  best  to  have  these  volumetric  solutions  of  a  definite,  even 
strength.  For  example,  the  potassium-permanganate  solution 
used  in  the  determination  of  iron  should  be  of  such  a  strength 
that  each  cubic  centimetre  will  equal  5  milligrammes  or  ia 


4  A   MANUAL   OF  PRACTICAL  ASSAYING. 

milligrammes  of  iron.  This  saves  a  great  deal  of  time,  and 
possibly  errors,  in  the. calculation  of  results. 

Use  apparatus  which  is  adapted  to  the  work,  and  never  use 
larger  apparatus  than  is  necessary.  For  example,  if  0.5  gm.  of 
slag  is  to  be  decomposed  by  acids,  if  introduced  into  a  large 
casserole  a  greater  quantity  of  acids  will  be  necessary  than  if  a 
small  casserole  is  used  and  the  operation  will  be  prolonged. 

Do  not  use  larger  filter-papers  than  are  necessary.  A  large 
filter  requires  much  more  washing  than  a  small  one. 

Be  careful  to  avoid  loss  in  boiling  and  other  operations. 

Never  accept  results  where  there  is  reason  to  believe  that 
they  may  be  incorrect,  owing  to  faulty  manipulation  or  acci- 
dents. •  • 


CHAPTER   II. 
SAMPLING. 

ALL  ores,  furnace  products,  etc.,  which  are  to  be  assayed 
must  be  first  accurately  sampled.  Accurate  sampling  is  quite 
as  essential  as  accurate  assaying;  for  if  the  sample  does  not 
truly  represent  the  lot  or  mass  from  which  it  was  taken,  the 
subsequent  assay  will  be  valueless. 

The  assayer  or  chemist  will  usually  receive  the  sample 
already  prepared  ;  but  as  he  will  occasionally  be  called  upon  to 
take  his  own  sample,  a  knowledge  of  the  art  of  sampling  and 
the  different  methods  in  vogue  is  essential. 

The  method  to  be  adopted  for  obtaining  a  sample  will  de- 
pend upon  the  character  of  the  material  to  be  sampled  and  the 
use  to  which  it  is  to  be  put  after  sampling :  for  example,  in 
the  case  of  a  silver  ore,  whether  the  ore  is  high  or  low  grade, 
whether  it  is  wet  or  dry,  etc.  If  the  ore  is  to  be  smelted,  it  is 
not  desirable  to  crush  it  finer  than  is  necessary  to  obtain  a 
correct  sample,  as  fine  ore  is  undesirable  for  smelting.  If  the 
ore  is  to  be  milled,  fine  crushing  is  not  a  disadvantage. 

It  is  hardly  necessary  to  say  that  in  obtaining  a  sample  the 
work  should  be  fairly  done,  no  discrimination  as  against  any 
portion  of  the  lot  or  mass  being  allowable. 

There  are  many  other  methods  of  sampling  besides  those 
described  in  the  following  pages,  but  the  methods  as  described 
are  standard  methods,  and  are  in  constant  use  in  many  of  our 
large  works,  having  been  tried  and  found  reliable. 

For  convenience  the  subject  may  be  considered  under  the 
following  headings  : 

1.  Ore  sampling. 

2.  Sampling  of  metallurgical  products. 

S 


O  A   MANUAL    OF  PRACTICAL  ASSAYING. 

Ore  Sampling. — A  proper  sampling  requires  adequate 
mixing,  impartial  selection  of  the  sample,  and  proper  relative 
comminution. 

The  different  methods  may  be  classified  as  follows: 

1.  Hand  sampling. 

2.  Combined  hand  and  mechanical  sampling. 

3.  Mechanical  sampling. 

The  first  two  methods  may  be  subdivided  into — • 

Fractional  selection  (tenth,  fifth,  etc.,  of  a  shovel). 

Quartering  (halving,  etc.). 

Split  shovel  (single,  double,  etc.,  scoop;  assayer's  riffles). 

Channelling  (driving  one  or  more  channels  through  a  pile ; 
driving  a  scoop  or  sampling  rod  through  a  pile  of  fine  ore, 
etc.). 

Mechanical  sampling  may  be  subdivided  into — 

1.  Continuous  sampling. 

2.  Intermittent  sampling. 

A  combination  of  one  or  more  of  these  methods  is  fre- 
quently adopted,  as  taking  every  tenth  shovel  from  the  car, 
crushing  this  sample,  and  reducing  it  by  quartering  or  split 
shovelling. 

Hand  sampling  consists  of  taking  a  sample  by  hand,  the 
only  tools  necessary  being  a  hammer,  mortar,  and  buckboard. 
Hand  or  grab  samples  are  frequently  taken  of  the  ores,  fuels, 
slags,  etc.,  at  metallurgical  works,  as  a  check  and  control  on  the 
metallurgical  operations.  In  taking  such  samples  care  should 
be  exercised  to  select  the  proper  relative  amount  of  fine  and 
coarse  material.  The  coarse  is  selected  by  chipping  pieces  from 
the  large  lumps.  Having  obtained  the  sample,  the  whole 
should  be  further  broken  to  the  proper  size  and  then  reduced 
by  quartering,  passing  over  a  split  shovel  or  over  assayer's 
riffles.  The  final  sample  should  be  ground  on  the  buckboard 
until  all  will  pass  through  an  eighty-mesh  sieve.  At  some 
works  the  practice  is  to  pass  all  samples  through  a  hundred- 
mesh  sieve.  The  finer  the  sample  is  reduced  the  better. 
Accurate  samples  can  be  taken  by  hand,  but  to  take  an  accu- 
rate sample  of  a  large  lot  of  ore  in  this  way  would  involve  an 


SAMPLING.  7 

immense  amount  of  labor ;  hence  the  second  and  third  methods 
of  sampling. 

COMBINED   HAND   AND   MECHANICAL    SAMPLING. 

This  method  of  sampling  can  be  carried  on  in  several  ways, 
as  illustrated  by  the  above  classification.  Just  which  method 
will  be  adopted  will  depend  upon  the  requirements  and  the 
facilities  in  each  individual  case.  Each  of  the  methods  gives 

O 

good  results,  provided  the  proper  precautions  are  observed. 
The  method  of  fractional  selection,  followed  by  comminution 
and  then  by  quartering  or  split  shovelling,  is  a  favorite  method 
with  many  smelting-works,  for  the  following  reasons  :  It  is 
desirable  that  the  bulk  of  the  ore  as  it  is  unloaded  from  the 
cars  or  ore-wagons  should  pass  directly  to  the  smelting  beds  or 
bins  with  a  minimum  amount  of  handling  (most  smelting-works 
make  no  charge  for  sampling),  and  also  that  the  bulk  of  the 
ore  should  remain  in  as  coarse  a  condition  as  is  consistent  with 
proper  sampling. 

This  method  is  as  follows :  As  the  ore-cars  are  unloaded 
every  tenth,  fifth,  third,  or  second  shovelful,  taken  indiscrimi- 
nately, is  thrown  into  a  wheelbarrow  as  a  sample.  In  case  the 
lot  contains  lumps  of  ore  which  are  too  large  for  the  shovel, 
they  should  be  broken  with  a  sledge-hammer  as  encountered. 
The  proportion  which  will  be  taken  for  a  sample  will  depend 
upon  the  character  of  the  ore.  In  the  case  of  a  high-grade 
silver  or  gold  ore,  ununiform  in  composition  (where  the  silver 
and  gold  is  unevenly  distributed  throughout  the  mass),  proper 
sampling  will  require  that  the  whole  lot  be  taken  for  sampling. 
In  the  case  of  low-grade  silver  or  gold  ores,  uniform  in  com- 
position, and  lead  or  copper  ores,  one  tenth  of  the  whole  will 
generally  give  a  fair  sample.  In  the  case  of  iron  ores,  other 
than  ores  which  may  be  classed  as  silver  and  gold  ores  on 
account  of  their  silver  and  gold  contents,  every  twentieth  or 
less  may  be  taken.  In  the  case  of  the  limestone  used  as  flux 
and  the  coal  and  coke,  a  much  smaller  proportion  maybe  taken; 
in  fact  a  fair  hand  sample  will  generally  answer. 


A   MANUAL    OF  PRACTICAL  ASSAYING. 

The  portion  taken  for  a  sample  is  removed  to  the  sampling, 
works  and  passed  through  the  crusher.  Should  the  sample 
weigh  about  10  tons,  it  can  now  be  safely  reduced  to  one  ton 
by  quartering,  except  in  the  case  of  very  high-grade  ores,  which 
are  ununiform  in  composition.  In  this  latter  case,  or  when 
the  sample  only  weighs  about  one  ton,  it  should  be  further 
comminuted  to  chestnut  size  by. passing  it  through  the  rolls. 

The  sample  can  be  reduced  in  bulk  by  any  of  the  methods 
classified  above,  preference  generally  being  given  to  quartering 
or  split-shovelling.  If  quartering  is  chosen,  the  ore  as  it  comes 
from  the  crusher  or  rolls  is  shovelled  into  a  conical  pile  on  the 
sampling-floor,  each  shovelful  being  thrown  on  the  apex  of  the 
cone.  When  the  cone  is  completed  it  is  flattened  out  by  com- 
mencing at  its  apex  with  a  shovel  and  passing  the  shovel 
around  in  the  path  of  a  spiral  until  the  whole  is  so  flattened 
that  it  will  be  from  6  to  12  inches  high,  and  present  the  appear- 
ance of  a  flat  cake  or  pie.  The  point  to  be  observed  here  is  to 
not  disturb  the  radial  distribution  of  the  coarse  and  fine  ore. 
It  is  now  divided  into  four  equal  quarters,  and  two  of  the 
diagonally  opposite  quarters  removed  to  one  of  the  bins  in  the 
sampling-works,  where  it  remains  until  the  lot  is  sampled  and 
settled  for.  It  is  convenient  to  retain  an  original  portion  of 
the  lot  for  resampling  in  case  of  a  dispute  between  seller  and 
buyer  on  the  first  sample.  The  remaining  quarters  are  now 
formed  into  a  conical  pile  by  alternately  shovelling  from  oppo- 
site quarters,  each  shovelful  being  thrown  on  the  apex  of  the 
pile.  This  cone  is  flattened  and  quartered  as  before,  the  opera- 
tion being  continued  until  the  remaining  portion  weighs  about 
200  pounds,  provided  the  sample  has  previously  been  crushed 
to  chestnut  size.  If  the  ore  has  not  been  previously  reduced 
to  chestnut  size  it  should  be  so  reduced  before  quartering  down 
to  200  pounds.  The  2OO-pound  sample  should  now  be  further 
comminuted  by  passing  it  through  a  small  set  of  rolls  set 
close.  It  is  now  further  reduced  by  quartering  until  it  weighs 
about  5  pounds.  This  5-pound  sample  should  now  be  dried 
on  a  steam  or  hot-air  bath,  and  when  thoroughly  dry  is  still 
further  comminuted  by  passing  through  a  coffee-mill  grinder, 


SAMPLING.  9 

The  product  of  the  coffee-mill  (about  2O-mesh)  is  how  reduced 
in  bulk  on  the  assayer's  riffle  or  by  quartering  until  we  have  a 
sample  weighing  from  I  to  3  pounds.  This  is  now  ground  on 
the  buckboard  until  it  will  all  pass  through  an  80  or  100  mesh 
sieve.  The  fine  pulp  is  then  spread  upon  a  piece  of  rubber  oil- 
cloth in  a  thin  layer,  and  the  sample  bottles  or  sacks  filled  by 
taking  portions  from  all  over  the  pile  on  the  point  of  a  steel 
spatula.  The  bottles  are  sealed  and  labelled,  the  works  always 
retaining  one  sample  as  an  umpire  in  case  of  dispute. 

In  case  the  split  shovel  is  adopted  the  process  is  essentially 
the  same,  except  that  the  ore  should  be  crushed  to  a  size  finer 
than  is  possible  in  the  crusher  before  using  the  split  shovel. 
The  following  points  are  to  be  observed  :  The  largest  particles 


FIG.  i. 

'*  JX 

FIG.  a. 

should  not  be  wider  than  one  fourth  of  the  width  of  the  scoop 
used ;  otherwise  when  they  strike  the  edges  of  the  scoop  they 
may  fly  out.  The  scoop  should  be  deep  enough  to  render  it 
impossible  for  pieces  striking  the  bottom  to  fly  out.  The 
material  should  be  thrown  or  delivered  on  the  scoop  squarely 
and  in  a  wide  flat  stream.  The  split  shovel  may  be  one  tenth 
as  wide  as  the  scoop  shovel  delivering  the  ore  to  it,  or  any  other 
width  which  may  be  desired.  The  split  shovels  are  made  so  as 
to  take  TV,  i,  £,  or  any  desired  amount  of  the  ore  delivered  to 
them,  as  is  shown  in  the  drawings. 

The  method  of  obtaining  a  sample  by  channelling  is  par- 
ticularly adapted  to  obtaining  a  sample  of  a  mine  dump  or  a 


10  A   MANUAL   OF  PRACTICAL   ASSAYING. 

large  pile  of  ore.  It  consists  in  running  one  or  more  channels 
or  cuts  through  the  pile,  taking  coarse  or  fine  as  it  comes.  This 
requires  that  the  contents  of  the  pile  should  have  been  pretty 
thoroughly  mixed  before  channelling.  If  such  is  not  the  case 
several  cuts  or  channels  should  be  run.  After  the  sample  is 
obtained  by  channelling  it  should  be  crushed  and  cut  down  as 
described  above.  Channelling  is  sometimes  adopted  in  place 
of  quartering  or  split-shovelling  after  the  ore  sample  has  been 
reduced.  It  answers  very  well  provided  the  pile  is  thoroughly 
mixed  before  channelling  each  time.  Samples  of  fine  ore,  such 
as  fine  concentrates  and  mill  tailings,  are  frequently  obtained  by 
driving  a  scoop  or  sampling-rod  into  the  pile  in  several  different 
places.  The  sampling-rod  consists  of  a  long  steel  rod  with  a 
semicircular  depression  in  one  side,  being  similar  to  the  samp- 
ling rod  used  by  sugar-samplers. 

MECHANICAL  SAMPLING. 

A  large  number  of  different  devices  for  obtaining  samples 
mechanically  have  been  invented.  These  all  depend  upon 
taking  the  sample  from  a  stream  of  falling  ore,  a  fractional  por- 
tion being  taken  for  the  sample.  The  process  may  be  contin- 
uous or  intermittent.  The  main  objections  to  all  automatic 
samplers  are :  The  difficulty  of  getting  at  the  apparatus  and 
cleaning  it  out  after  each  lot  is  run  through.  This  is  a  serious 
difficulty  with  some  of  the  devices,  as  it  will  not  do  to  run  a 
low-grade  galena,  low  in  silver,  through  the  apparatus  which 
has  just  previously  sampled  a  high-grade  silver  or  gold  ore, 
unless  the  apparatus  has  been  previously  thoroughly  cleaned. 
Another  objection  is  that  the  ore  is  not  in  full  view  during  all 
stages  of  the  process.  Another  objection  amongst  smelters  is 
that  it  requires  the  whole  sample  to  be  crushed  to  a  certain 
degree  of  fineness  before  it  is  run  through  the  sampler.  How- 
ever, with  proper  care  automatic  samplers  give  good  results, 
and  have  the  great  advantage  that  the  work  is  done  mechani- 
cally and  indiscriminately.  The  general  scheme  with  the  con- 
tinuous samplers  is  as  follows :  The  ore  is  fed  into  a  crusher, 


SAMPLING.  1 1 

from  which  it  passes  through  rolls.  It  is  then  elevated  mechani- 
cally to  a  bin,  from  which  it  falls  into  a  long  vertical  chute, 
where  it  is  again  mixed  by  rods  or  points  in  the  chute.  At  a 
suitable  point  in  the  chute  some  device  is  introduced  to  take 
out  a  fractional  portion  of  the  falling  stream.  The  fractional 
portion  is  frequently  passed  through  a  second  set  of  rolls  placed 
so  as  to  crush  finer  than  the  first  set,  and  again  through  some 
device,  similar  to  the  above,  which  takes  out  a  fractional  por- 
tion. This  portion  is  then  passed  through  a  coffee-mill,  bucked, 
and  treated  as  before.  This  process  requires  that  the  ore 
should  be  quite  dry  before  it  is  run  through  the  mill.  This 
method  is  a  favorite  one  with  some  smelters  for  sampling  low- 
grade  sulphide  ores  and  mattes  which  are  roasted  previous  to 
smelting.  In  this  case  the  fineness  of  the  ore  is  no  objection, 
as  the  ore  would  have  to  be  reduced  to  a  certain  degree  of 
fineness  before  roasting. 

Intermittent  samplers  take  a  portion  of  the  ore,  fractional 
or  otherwise,  at  intervals.  The  time  between  these  intervals 
may  be  controlled  mechanically,  so  that  the  intervals  will  be  of 
equal  duration.  Many  devices,  such  as  intercepting-buckets, 
which  intercept  certain  quantities  at  stated  intervals,  have  been 
invented. 

A  modification  of  the  method  of  taking  a  fractional  portion 
from  a  continuous  stream  of  falling  ore  has  lately  been  intro- 
duced by  The  Denver  Public  Sampling  Works  which  presents 
some  advantages.  The  method  as  practised  by  these  works  is 
essentially  as  follows :  All  of  the  lot,  or  such  fractional  portion 
as  is  deemed  necessary,  is  passed  through  the  crusher  and  rolls. 
From  the  rolls  it  is  raised  to  the  upper  floor  of  the  mill  by  an 
elevator,  which  discharges  into  an  iron  hopper  which  is  above 
the  floor  level  and  easily  accessible  for  inspection  and  cleaning. 
This  hopper  is  shown  in  Fig.  3. 

The  bottom  of  the  hopper  is  connected  with  a  vertical 
chute  about  18  inches  long,  which  is  closed  by  a  slide-gate  (a). 
At  the  bottom  of  the  chute  is  a  sheet-iron  chute  (b)  which 
diverts  a  portion  of  the  ore  to  one  side  when  the  gate  (a)  is 
opened.  Penetrating  through  this  chute  is  a  trough  (c)  similar 


12 


A   MANUAL   OF  PRACTICAL   ASSAYING. 


to  the  scoop  of  a  split  shovel,  the  width  of  this  trough  being 
one  tenth  of  the  width  of  the  chute.  When  the  gate  (a)  is 
opened  nine  tenths  of  the  ore  is  diverted  to  one  side  by  the 
chute  (b)  into  a  car  or  wheelbarrow,  and  one  tenth  (the  sample) 
to  the  opposite  side  by  the  trough  (c).  This  sample  is  then 
reduced  in  bulk  by  split-shovelling  to  about  200  pounds,  which 
is  passed  through  a  small  set  of  rolls,  after  which  it  is  reduced 


a 


FIG.  3. 


by  the  assayer's  riffle,  and  is  finally  ground  in  the  coffee-mill, 
bucked,  etc.,  as  before. 

Many  devices  for  the  taking  of  intermittent  samples,  such 
as  intercepting-buckets,  which  intercept  certain  quantities  at 
stated  times,  have  been  invented.  One  of  the  best  of  the 
automatic  samplers  is  that  devised  by  D.  W.  Brunton,  of  Aspen, 
Colo.,*  which  is  shown  in  Fig.  4.  This  device,  in  place  of 
taking  out  a  portion  of  the  falling  stream  of  ore,  diverts  the 
whole  stream  during  certain  intervals.  These  intervals  may  be 
regulated,  as  required,  so  as  to  obtain  10,  20,  etc.,  per  cent  of 
the  ore  for  a  sample  by  a  simple  device.  As  the  stream  of 
ore  is  neither  split  nor  divided,  fine  crushing  on  large  samples 
is  entirely  unnecessary.  After  the  ore  has  been  crushed  it  is 
elevated  a  few  feet  above  the  level  of  the  storage-bins  and 


*  Transactions  of  the  American  Institute  of  Mining  Engineers,  Vol.  XIII, 
p.  639. 


SAMPLING. 


discharged  into  the  sampler,  Fig.  4,  in  which  C  is  a  vertical 
or  inclined  chute,  containing 
the  falling  stream  of  ore.  B 
is  a  funnel  for  narrowing  the 
width  of  the  falling  stream,  so 
as  to  reduce  to  a  minimum  the 
necessary  travel  of  the  deflect- 
ing-chute  A.  This  chute  A  is 
pivoted  upon  a  rock-shaft. 
When  it  is  deflected  to  the  right 
the  entire  stream  of  ore  is 
thrown  into  E,  and  when  it  vis 
deflected  to  the  left  the  entire 
stream  is  thrown  into  D.  The 
driving-bar./ receives  its  motion 
from  the  pins  L  in  the  face  of  the 
driving-wheel//,  which  is  driven 


FIG.  4. 


by  the  pulley  G.  The  face  of  the  wheel  H  is  perforated  by 
two  rows  of  holes,  the  distance  between  the  two  rows  being 
the  same  as  the  necessary  movement  of  the  crank.  In  these 
holes  are  inserted  a  number  of  pins  L  held  in  place  by  jam-nuts 
on  the  interior  of  the  wheel-face.  Preferably  20  holes  are 
bored  in  each  row,  each  hole  or  pin  representing  5  per  cent 
of  the  time  necessary  for  a  complete  revolution  of  the 
wheel. 

Now,  if  50  per  cent  of  the  pins  are  placed  in  the  right-hand 
row  of  holes,  and  50  per  cent  in  the  left-hand  row,  then  the 
revolution  of  the  wheel  H  carrying  the  pins  L  through  the 
guides  NN  on  the  driving-bar  J  will  hold  the  deflecting-chute 
A  on  the  right  during  one  half  revolution  and  on  the  left 
during  the  other  half,  thus  dividing  the  stream  into  two  equal 
portions.  If  20  per  cent  of  the  pins  are  placed  in  the  right- 
hand  row  and  80  per  cent  in  the  left,  then  the  deflecting-chute 
A  will  be  held  on  the  right  during  one  fifth  of  a  revolution  and 
on  the  left  during  four  fifths,  thus  throwing  20  per  cent  of  the 
ore  into  spout  E  and  80  per  cent  into  spout  D,  etc.  The  ore 
falling  into  E  passes  into  the  storage-bins,  whilst  the  ore  falling 


14  A    MANUAL    OF  PRACTICAL   ASSAYING. 

into  D  is  discharged  through  a  spout  into  a  set  of  rolls  situated 
on  the  same  level  as  the  breaker. 

After  being  fine-crushed  by  the  rolls,  the  sample  is  raised 
by  an  elevator  to  the  same  level  as  at  first,  and  drops  through 
a  second  divider,  similar  to  the  first,  set  to  any  desired  amount 
per  cent. 

The  rejected  ore  falls  into  the  bin  with  the  ore  from  which 
it  was  first  separated,  and  the  final  sample  drops  into  a  closed 
and  locked  bin  on  the  working  floor  below. 

All  of  these  devices  require  thorough  cleaning  after  each 
lot  is  run  through  and  after  one  lot  is  finished.  Before  com- 
mencing on  a  new  lot  it  is  best  to  run  through  some  of  the  new 
lot  (this  portion  not  to  be  mixed  with  the  sample)  in  order  to 
thoroughly  cleanse  the  apparatus. 

In  handling  wet  or  frozen  ore  it  can  generally  be  cut  down 
to  about  one  ton  before  drying.  At  this  point  it  is  best  to  dry 
the  sample  before  proceeding  further.  Before  grinding  in  the 
coffee-mill  the  sample  should  be  thoroughly  dried,  the  oven 
of  an  ordinary  cook-stove  being  a  very  satisfactory  piece  of 
apparatus  for  this  purpose. 

Dr.  S.  A.  Reed,  in  The  School  of  Mines  Quarterly,  Vol.  VI, 
No.  4,  discusses  the  subject  of  ore-sampling  mathematically, 
and  deduces  some  interesting  formulae. 

SAMPLING  OF   METALLURGICAL  PRODUCTS. 

Pig-iron. — The  drillings  are  usually  taken  from  the  frac- 
tured end  of  a  pig.  In  order  to  protect  the  sample  from  slag, 
sand,  etc.,  the  end  of  the  pig  is  covered  by  wrapping  around  it 

a  piece  of  heavy  paper.  As  the 
pigs  are  seldom  perfectly  homo- 
geneous, especially  if  the  iron  con- 
tains much  sulphur,  phosphorus,  or 
manganese,  it  is  best  to  take  several 

drillings,  at  the  points  indicated  in  the  sketch,  and  thoroughly 
mix  them  together  for  the  sample. 

Base  Bullion. — Base  or  silver-lead  bullion,  if  pure,  would 
be  an  alloy  of  lead  with  small  quantities  of  silver  and  gold. 


SAMPLING.  15 

However,  it  is  seldom  pure,  and  may  contain  copper,  zinc,  bis- 
muth, arsenic,  antimony,  sulphur,  etc. 

In  many  of  our  smelting-works  the  custom  is  to  ladle  directly 
from  the  lead-well  of  the  blast-furnace  into  the  bullion  mould. 
If  this  method  is  adopted  the  resulting  bars  of  bullion  will  nec- 
essarily contain  nearly  all  the  impurities  of  the  lead.  At  some 
works  the  practice  is  to  tap  the  lead-well,  or  ladle  off  the  lead 
into  a  cooling  kettle.  This  kettle  is  of  cast-iron,  heated  under- 
neath by  a  coal  fire,  and  capable  of  holding  from  600  to  1200 
pounds  of  lead.  When  the  cooling  pot  is  used  the  following  is 
the  method  of  procedure  :  From  500  to  1000  pounds  of  lead  is 
tapped  or  ladled  into  the  cooling  pot,  which  has  previously 
been  heated,  and  is  kept  at  a  proper  temperature  by  the  char- 
coal fire  underneath  the  kettle.  The  bullion  in  the  kettle  is 
stirred  and  skimmed,  the  skimmings  being  returned  to  the 
blast-furnace,  together  with  the  ore  charge.  This  is  by  far 
the  best  method  of  casting,  as  considerable  of  the  dross  of  the 
bullion  is  removed,  and  the  bars  are  cleaner  and  more  uniform. 
The  bullion  is  cast  in  moulds  of  such  size  that  the  resulting 
bars  of  bullion  will  weigh  about  100  pounds. 

It  is  a  well-known  fact  that  if  an  alloy  of  lead,  silver,  and 
gold  be  cast  into  a  bar  the  different  parts  of  the  bar,  owing  to 
the  sudden  chilling,  will  contain  different  proportions  of  silver 
and  gold. 

This  fact  is  illustrated  by  the  "  Pattison  Process  "  of  de- 
silverization.  If  the  alloy  contains  zinc,  copper,  sulphur,  etc. 
(any  or  all  of  which  most  bullion  contains),  the  percentage  of 
silver  and  gold  in  different  parts  of  the  bar  will  vary  to  a  much 
greater  extent  than  in  the  previous  case.  The  method  of 
"  zinc  desilverization "  is  a  partial  illustration  of  this  fact. 
These  facts  render  the  sampling  of  the  bullion  a  difficult  mat- 
ter if  it  is  at  all  rich  in  silver  or  gold. 

The  method  of  sampling  as  described  below  has  been 
adopted  by  many  of  the  large  smelting  and  refining  works  of 
the  United  States,  and  it  is  believed  that  it  obviates  most  of 
the  difficulties  heretofore  experienced  by  smelters  and  re- 
finers in  arriving  at  a  correct  sample  of  the  lot  of  bullion. 


i6 


A   MANUAL    OF  PRACTICAL   ASSAYING. 


The  pigs  of  bullion  in  series  of  five  are  weighed  by  the 
sampler,  the  weight  being  noted  and  the  lot  number  being 
stamped  on  each  pig  as  shown  in  Fig.  5.  The  pigs  are 
unloaded  on  the  sampling  platform,  as  shown  in  Fig.  5. 

The  samples  are  taken  by  meams  of  a  steel  punch  similar 
to  a  belt  punch,  but  larger,  shown  in  Fig.  6.  This  punch  is 
about  14  inches  long,  and  is  made  of  i-inch  to  ij-inch  steel,  so 
arranged  that  when  driven  into  the  bar  of  bullion  it  will  take 
out  a  core  about  •§•  inch  in  diameter  and  in  length  equal  to  half 
the  thickness  of  the  bar  of  bullion.  The  head-sampler  usually 
holds  and  directs  the  punch  whilst  his  assistant  strikes  it  with 
a  sledge.  In  order  to  insure  a  uniform  sample  it  is  essential 
that  the  punch  should  be  driven  half  through  the  bar  in  each 
case,  so  that  the  length  of  the  core  should  be  equal  to  half  the 
thickness  of  the  bar.  The  samples  are  taken  from  each  pig  at 
a,  b,  c,  d,  and  e.  The  pigs  are  then  turned  over,  and  five 


°j 


FIG.  <;. 


FIG.  6. 


fr  " 


FIG.  7. 

samples  taken  from  the  bottom  side  of  each  pig  in  the  reverse 
order,  as  shown  at  f,g,  c,  h,  and/.  At  some  works  it  is  the 
custom  to  dip  the  punch  in  oil,  in  order  to  make  it  drive  easier. 
This  practice  is  to  be  condemned,  as  dipping  in  water  answers 
the  same  purpose,  and  oil  greases  the  cores  so  that  they  are 
liable  to  take  up  any  dirt  or  particles  of  dust  (which  are  always 
present  in  a  smelting-works),  which  are  liable  to  affect  the 


SAMPLING.  \f 

sample.     Oil  also  makes  a  bad  scum  and  has  a  tendency  to 
affect  the  sample  in  melting. 

A  car-load  of  bullion  generally  contains  280  pigs.  When 
the  sampling  of  the  lot  is  finished  the  560  cores  are  taken  to 
the  assay  office  for  melting  and  assay. 

The  cores  are  melted  in  a  clean  graphite  crucible,  which 
should  not  be  more  than  two-thirds  full  when  the  sample  is 
melted  down.  The  melting  should  be  carefully  conducted, 
the  temperature  being  gradually  raised.  It  is  essential  that 
the  temperature  should  be  sufficiently  high  at  the  last,  so  that 
the  mass  will  be  perfectly  fluid  ;  but,  on  the  other  hand,  the 
temperature  should  not  be  raised  to  such  a  point  that  the  lead 
will  cupel  or  scorify,  as  this  would  result  in  the  loss  of  lead, 
and  consequent  enrichment  of  the  sample  in  silver  and  gold. 

When  the  sample  is  melted  and  perfectly  fluid,  the  crucible 
is  removed  from  the  furnace,  its  contents  thoroughly  stirred 
with  a  clean  iron  rod,  and  poured  into  an  iron  mould.  The 
mould  should  be  of  such  a  size  that  the  resulting  bar  will  be 
about  10  inches  long,  2\  inches  wide,  and  f  inch  thick.  The 
sample  should  not  be  skimmed  before  pouring,  as,  if  the  melt- 
ing is  conducted  at  the  proper  temperature  and  not  unduly 
prolonged,  very  little  dross  will  rise  upon  the  surface  of  the 
lead.  When  cool,  the  bar  is  removed  from  the  mould  and 
four  samples  are  cut  from  it  for  assay,  as  shown  in  Fig.  7.  The 
sample  bar  is  stamped  with  the  lot  number  of  the  bullion,  and 
retained  until  the  lot  is  settled  for. 

In  the  case  of  very  rich  and  extremely  impure  bullion  the 
following  method  may  be  necessary,  although  in  several  years 
experience  the  author  has  only  had  occasion  to  use  this  method 
a  few  times. 

Special  Method. — When  a  large  amount  of  dross  is  formed 
it  should  be  removed  by  skimming  with  a  perforated  skimmer, 
allowing  the  lead  to  drain  back  into  the  crucible.  Place  all 
the  dross  in  an  iron  sample  pan  and  reserve.  Now  pour  the 
clean  lead  into  the  mould,  and  when  cool  remove  the  bar  and 
weigh  it.  After  weighing,  sample  the  bar  by  taking  four 
samples,  as  shown  above. 


1 8  A   MANUAL   OF  PRACTICAL  ASSAYING. 

Weigh  the  dross,  and,  after  weighing,  break  it  up  on  the 
bucking-board  and  thoroughly  sample  it,  taking  four  samples 
of  J  A.  T.  each,  for  assay.  (For  the  assay  and  calculation,  see 
Chapter  I,  Part  III.) 

Slags. — Lead  and  copper  furnace  slags  may  be  sampled  by 
any  of  the  following  methods  : 

First.  After  the  slag-pot  is  removed  from  the  furnace  it  is 
allowed  to  cool  until  a  thin  crust  forms  on  the  top  of  the  slag. 
The  crust  is  broken  and  removed  with  a  bar.  The  end  of  a 
clean  steel  bar  about  one  inch  in  diameter  is  then  plunged  into 
the  hot  slag  to  a  depth  of  about  three  inches  and  in  a  few  sec- 
onds withdrawn,  and  the  end  of  the  bar  with  the  thin  coating 
of  slag  adhering  to  it  is  plunged  into  water  to  cool  or  chill  the 
slag  quickly.  The  sample  should  be  brittle  and  vitreous 
throughout.  If  not  brittle  and  vitreous  it  should  be  rejected. 
Samples  may  be  taken  as  frequently  as  desired,  the  separate 
samples  being  bucked  down  together  and  passed  through  a 
loo-mesh  sieve. 

Second.  Some  works  prefer  to  take  the  samples  in  a  small 
ladle  as  the  slag  runs  from  the  spout  of  the  furnace.  These 
samples  are  usually  taken  at  stated  intervals,  and  just  after  the 
furnace  has  been  tapped  for  matte.  They  may  be  poured 
into  water  from  the  ladle,  in  order  to  make  them  vitreous  and 
granulated,  which  facilitates  the  subsequent  pulverization. 

Third.  Some  works  prefer  to  take  the  sample  from  the 
cold  cones  of  slag  on  the  dump.  The  samples  should  be  taken 
from  the  centre  and  above  the  matte,  and  about  a  third  way 
from  the  edge  towards  the  centre.  These  samples  are  taken 
with  a  small  hammer,  after  breaking  the  cone  up  with  a 
sledge. 

The  first  method  presents  many  advantages,  as  it  lessens 
the  labor  required  in  pulverizing  the  sample,  and  also — at  least 
in  the  case  of  lead  and  copper  slags — converts  the  slag  into  a 
form  which  is  soluble  in  acids.* 

Silver  Bullion. — If  the  silver  is  remelted  before  casting 
into  bars,  one  of  the  following  methods  may  be  adopted  : 

*  Determination  of  silica,  Part  II,  Chap.  I. 


SAMPLING.  19 

First.  Just  before  pouring,  the  contents  of  the  crucible  are 
thoroughly  stirred  with  an  iron  rod.  The  sample  is  now  taken 
from  the  centre  of  the  crucible  by  means  of  a  sampling-cup, 
which  consists  of  a  small  steel  cup  provided  with  a  cover  which 
fits  tight  when  inserted  in  the  cup.  The  cup  and  cover  are 
provided  with  long  iron  handles.  Before  using,  the  cup  and 
cover  should  be  heated.  The  cover  is  now  put  on  the  cup  and 
the  apparatus  inserted  into  the  centre  of  the  molten  silver. 
The  cover  is  now  withdrawn  and  the  cup  allowed  to  fill  with 
silver,  when  the  cover  is  replaced  by  means  of  the  handle,  the 
apparatus  removed  from  the  crucible,  and  the  silver  which  the 
cup  contains  poured  into  water  in  order  to  granulate  it. 

Second.  Just  after  commencing  to  pour  the  silver  out  of 
the  crucible  into  the  moulds  some  of  the  silver  is  caught  in  a 
small  ladle.  This  operation  is  repeated  when  about  half  the 
silver  has  been  poured,  and  again  when  nearly  all  has  been 
poured  out.  Each  of  the  samples  is  granulated  in  water. 

This  method  of  sampling  also  answers  where  the  silver  is 
tapped  directly  from  the  cupel  furnace  into  the  moulds,  a 
sample  being  taken  just  after  the  silver  begins  to  run,  another 
when  about  one  half  has  run  out,  and  a  third  just  before  all 
the  silver  has  run  out. 

These  are  about  the  only  methods  which  are  to  be  recom- 
mended. The  taking  of  a  sample  from  the  ends  or  corners  of 
the  bar  by  chipping  will  not  give  a  fair  sample  unless  the  sil- 
ver is  very  pure,  nearly  1000  fine.  If  the  silver  has  copper  or 
other  base  metal  alloyed  with  it,  different  portions  of  the  bar 
will  vary  considerably  in  their  composition. 

Gold  Bullion. — The  weighed  gold  is  melted  in  a  graphite 
crucible  with  suitable  fluxes,  the  slag  skimmed  off,  after  which 
it  is  thoroughly  mixed  by  stirring  and  poured  into  a  mould. 
Samples  are  now  cut  from  the  top  and  bottom  of  the  bar. 
These  samples  should  agree  in  fineness  if  the  work  of  melting 
has  been  well  done.  In  the  U.  S.  mints  and  assay  offices  the 
practice  is  to  weigh  before  and  after  melting,  the  difference  in 
weight  being  reported  as  the  loss  in  melting. 

Mattes. — They  can  be  sampled  in  the  same  manner  as  ore. 


20  A    MANUAL   OF  PRACTICAL  ASSAYING. 

Automatic  sampling  answers  very  well,  as  the  matte  has  to  be 
finely  pulverized  prior  to  roasting. 

Flue  Dust. — Sampled  the  same  as  ore.  As  it  is  mostly  in 
a  fine  state,  the  taking  of  every  tenth  shovelful  as  a  sample, 
when  cleaning  out  the  flues,  answers  very  well. 

Concentrates. — Concentrates  from  milling  operations  are 
sampled  in  the  same  manner  as  ore.  Being  in  a  finely  pulver- 
ized state,  they  present  no  difficulties. 

Tailings.  —  Tailings  from  milling  operations  may  be 
sampled  the  same  as  concentrates  if  there  is  a  pile  or  heap. 
When  the  tailings  are  allowed  to  run  into  a  neighboring 
stream  samples  should  be  taken  from  the  tail-box  at  intervals. 
An  automatic  device  may  be  arranged  for  this  purpose. 

Silver  Precipitate. — The  precipitated  silver  from  a  leach- 
ing works  consists  of  sulphide  of  silver  mixed  with  impurities, 
principally  sulphides.  To  obtain  a  correct  sample  of  this 
material,  which  runs  from  4000  to  14,000  ounces  of  silver  per 
ton,  is  a  difficult  matter.  The  following  method  answers  very 
well,  if  carefully  carried  out :  Spread  the  material  upon  a  clean 
iron  floor  and  divide  into  a  number  of  squares  about  one  foot 
square.  From  each  square  take  five  samples,  putting  all  these 
samples  in  a  pile.  The  pile  should  be  thoroughly  mixed,  and 
then  spread  out  and  reduced  as  before.  The  final  sample,  of 
about  five  pounds,  should  be  pulverized  in  the  coffee-mill  and 
still  further  reduced,  the  final  sample  being  bucked  on  a  buck- 
ing-board until  it  will  all  pass  through  an  80-  or  loo-mesh 
sieve. 

Copper  Ingots. — Pig-copper  is  usually  sampled  by  drilling 
through  the  pigs  from  top  to  bottom.  The  top  and  bottom 
drillings  being  a  mixture  of  slag  and  oxides  come  out  as  a 
powder,  whilst  the  inside  being  malleable  comes  out  in  the 
form  of  strings.  A  good  plan  is  to  put  the  drillings  in  a  glass 
bottle  and  then  operate  upon  the  strings  with  a  pair  of  scissors 
until  the  large  drillings  are  all  chopped  up  fine,  then  quarter. 


CHAPTER    III. 
PRELIMINARY   EXAMINATION. 

ALL  material  submitted  to  the  assayer  for  analysis  shoulu 
first  undergo  a  preliminary  examination,  to  determine  its  char- 
acter and  principal  constituents.  A  little  time  spent  in  this 
manner  will  frequently  result  in  a  great  saving  of  time  in  the 
subsequent  analysis.  If  the  character  of  the  material  is  not 
understood  a  wrong  method  of  analysis  may  be  adopted,  or  a 
substance  may  be  analyzed  for  some  constituent  which  is  pres- 
ent in  such  small  quantities  that  its  determination  is  unneces- 
sary. Sometimes  this  preliminary  examination  is  unnecessary,, 
as  when  a  substance  for  analysis  is  submitted  with  a  statement 
of  its  character  and  the  constituents  required  to  be  deter- 
mined. It  frequently  happens  that  the  assayer  receives  a 
substance  with  the  request  that  its  chief  constituents  be  deter- 
mined, in  which  case  a  few  qualitative  tests  will  generally  be  a. 
sufficient  guide.  In  the  case  of  an  ore  in  lump  form,  the 
assayer  will  be  able  to  determine  its  chief  constituents  by  an 
eye  examination  and,  possibly,  a  few  tests  with  the  blowpipe. 

In  most  of  our  metallurgical  works  the  assayer  generally 
receives  the  sample  for  assay  already  pulverized.  In  this  case 
the  chief  constituents  and  the  character  of  the  material  can 
generally  be  determined  readily  by  treating  the  sample  as  fol- 
lows :  Place  about  half  a  gramme  of  the  sample  on  a  large 
watch-glass,  and  van  with  a  little  water,  by  rotating  and  gently 
tapping  the  edge  of  the  glass,  so  as  to  separate  the  lighter 
from  the  heavier  particles.  After  thus  separating  the  par- 
ticles, an  examination  with  the  aid  of  a  magnifying-glass  will- 
show  the  principal  mineral  constituents  and  their  approximate 
amounts.  The  author  has  found  this  an  invaluable  aid  in 


22  A   MANUAL    OF  PRACTICAL    ASSAYING. 

determining  what  the  sample  should  be  analyzed  for,  and  also 
the  method  of  analysis  to  be  pursued.  For  example,  the  pulver- 
ized sample  may  show  the  ore  to  be  oxidized,  but  upon  van- 
ning it  will  be  found  to  contain  small  particles  of  sulphides. 

For  the  preliminary  testing  of  ores  and  furnace  products 
and  the  testing  of  buttons  and  precipitates  the  blowpipe  is 
extremely  valuable.  Any  intelligent  assayer,  with  a  little 
practice,  can  become  sufficiently  familiar  with  the  ordinary 
blowpipe  tests. 

The  following  list  of  blowpipe  tests  is  taken  from  an  article 
by  Prof.  A.  J.  Moses,*  and  gives  all  of  the  tests  necessary  for 
the  preliminary  examination,  by  means  of  the  blowpipe,  of 
ores,  metallurgical  products,  etc. 

BLOWPIPE  TESTS. 

The  details  in  ordinary  manipulations,  such  as  obtaining 
beads,  flames,  coatings,  and  sublimates,  are  omitted,  and  the 
results  alone  stated.  Unusual  manipulations  are  described. 
The  bead  tests  are  supposed  to  be  obtained  with  oxides  ;  the 
other  tests  are  in  general  true  of  all  compounds  not  expressly 
excluded.  The  course  to  be  followed  in  the  case  of  interfering 
elements  is  briefly  stated. 

Aluminium,  Al. 

With  Soda. — Swells  and  forms  an  infusible  compound. 

With  Borax  or  S.  Ph. — Clear  or  cloudy,  never  opaque. 

With  Cobalt  Solution. — Fine  blue  when  cold.  (Certain 
phosphates,  borates,  and  fusible  silicates  become  blue  in  ab- 
sence of  alumina.) 

Ammonia,  NH3. 

In  Closed  Tube. — Evolution  of  gas  with  the  characteristic 
odor.  Soda  or  lime  assists  the  reaction.  The  gas  turns  red 
litmus-paper  blue,  and  forms  white  clouds  with  HC1  vapor. 

*  Summary  of  Useful  Tests  with  the  Blowpipe.      School  of  Mines  Quar- 
terly, Vol.  XI,  No.  i. 


FKKLfMINARY  EXAMINATION.  2$ 

Antimony,  Sb. 

On  Coal,  R.  F. — Volatile  white  coat,  bluish  in  thin  layers, 
continues  to  form  after  cessation  of  blast.  (This  coat  may  be 
further  tested  by  S.  Ph.  or  flame.) 

With  Bismuth  Flux  : — On  Plaster. — Orange-red  coat,  made 
orange  by  (NH4)2S. 

On  Coal. — Faint  yellow  or  red  coat. 

In  Open  Tube. — Dense,  white,  non-volatile,  amorphous  sub- 
limate. The  sulphide,  too  rapidly  heated,  will  yield  spots  of 
red. 

In  Closed  Tube. — The  oxide  will  yield  a  white  fusible  subli- 
mate of  needle  crystals ;  the  sulphide,  a  black  sublimate,  red 
when  cold. 

Flame. — Pale  yellow-green. 

With  S.  Ph. — Dissolved  by  O.  F.,  and  treated  on  coal  with 
tin  in  R.  F.  becomes  gray  to  black. 

Interfering  Elements. 

Arsenic. — Remove  by  gentle  O.  F.  on  coal. 

Arsenic  with  Sulphur. — Remove  by  gently  heating  in  closed 
tube. 

Copper. — The  S.  Ph.  bead  with  tin  in  R.  F.  may  be  momen- 
tarily red,  but  will  blacken. 

Lead  or  Bismuth. — Retards  formation  of  their  coats  by  inter- 
mittent blast,  or  by  boracic  acid.  Confirm  coat  by  flame,  not 
by  S.  Ph. 

Arsenic,  As. 

On  Smoked  Plaster.— White  coat  of  octahedral  crystals. 

On  Coat.— Very  volatile  white  coat  and  strong  garlic  odor. 
The  oxide  and  sulphide  should  be  mixed  with  soda. 

With  Bismuth  Flux :— On  Plaster.— Reddish-orange  coat, 
made  yellow  by  (NH4)flS. 

On  GW.— Faint-yellow  coat. 

In    Open    Tube.— White  sublimate   of   octahedral   crystals. 


24  A   MANUAL    OF  PRACTICAL  ASSAYING. 

Too  high  heat  may  form  brown  suboxide  or  red  or  yellow 
sulphide. 

In  Closed  Tube. — May  obtain  white  oxide,  yellow  or  red 
sulphide,  or  black  mirror  of  metal. 

Flame. — Pale  azure-blue. 


Interfering  Elements. 

Antimony. — Heat  in  closed  tube  with  soda  and  charcoal, 
treat  resulting  mirror  in  O.  F.  for  odor. 

Cobalt  or  Nickel. — Fuse  in  O.  F.  with  lead  and  recognize  by 
odor. 

Sulphur. — (a)  Red  to  yellow  sublimate  of  sulphide  of  arsenic 
in  closed  tube. 

(b)  Odor  when  fused  with  soda  on  coal. 

Barium,  Ba. 

On  Coal,  with  Soda. — Fuses  and  sinks  into  the  coal. 

Flame. — Yellowish  green,  improved  by  moistening  with 
HC1. 

With  Borax  or  S.  Ph. — Clear  and  colorless ;  can  be  flamed 
opaque  white. 

Bismuth,  Bi. 

On  Coal. — In  either  flame  is  reduced  to  brittle  metal  and 
yields  a  volatile  coat,  dark  orange-yellow  hot,  lemon-yellow 
cold,  with  yellowish-white  border. 

With  Bismuth  Flux  (sulphur,  2  parts ;  potassic  iodide,  I 
part ;  potassic  bisulphate,  I  part) : — On  Plaster. — Bright-scarlet 
coat  surrounded  by  chocolate-brown  with  sometimes  a  reddish 
border.  The  brown  may  be  made  red  by  ammonia.  (May  be 
obtained  by  heating  S.  Ph.  on  the  assay.) 

On  Coal. — Bright-red  coat  with  sometimes  an  inner  fringe 
of  yellow. 

With  S.  Ph. — Dissolved  by  O.  F.  and  treated  on  coal  with 
tin  in  R.  F.  is  colorless  hot,  but  blackish  gray  and  opaque  cold. 


PRELIMINARY  EXAMINATION.  2$ 

Interfering  Elements. 

Antimony. — Treat  on  coal  with  boracic  acid,  and  treat  the 
resulting  slag  on  plaster  with  bismuth  flux. 
Lead. — Dissolve  coat  in  S.  Ph.,  as  above. 

Boron,  B. 

All  borates  intumesce  and  fuse  to  a  bead. 

Flame. — Yellowish  green.  May  be  assisted  by :  (a)  Moisten- 
ing with  H3SO4 ;  (b)  Mixing  to  paste  with  water,  and  boracic- 
acid  flux  (4%  parts  KHSO4 ,  I  part  CaF2) ;  (c)  By  mixing  to 
paste  with  HaSO4  and  NH4F. 

Bromine,  Br. 

With  S.  Ph.,  saturated  with  CuO. — Treated  at  tip  of  blue 
£ame,  the  bead  will  be  surrounded  by  greenish-blue  flame. 
In  Matrass  with  KHSO±. — Brown,  choking  vapor. 

Interfering  Elements. 

Silver. — The  bromine  melts  in  KHSO4  and  forms  a  blood- 
red  globule,  which  cools  yellow  and  becomes  green  in  the 
sunlight. 

Cadmium,  Cd. 

On  Coal,  R.  F. — Dark-brown  coat,  greenish  yellow  in  thin 
layers.  Beyond  the  coat,  at  first  part  of  operation,  the  coal 
shows  a  variegated  tarnish. 

On  Smoked  Plaster  with  Bismuth  Flux. — White  coat  made 
orange  by  (NH4)2S. 

With  Borax  or  S.  Ph. — O.  F.  Clear  yellow  hot,  colorless 
cold ;  can  be  flamed  milk-white.  The  hot  bead  touched  to 
Na2SQO3  becomes  yellow. 

R.  F.  Becomes  slowly  colorless. 

Interfering  Elements. 

Lead,  Bismuth,  Zinc. — Collect  the  coat,  mix  with  charcoal 
dust,  and  heat  gently  in  a  closed  tube.  Cadmium  will  yield 


26  A   MANUAL   OF  PRACTICAL  ASSAYING. 

cither  a  reddish  -  brown   ring  or  a  metallic  mirror.       Before 
collecting  coat  treat  it  with  O.  F.  to  remove  arsenic. 

Calcium,  Ca. 

On  Coal,  with  Soda. — Insoluble,  and  not  absorbed  by  the 
coal. 

Flame. — Yellowish  red,  improved  by  moistening  with  HC1. 

With  Borax  or  S.  Ph. — Clear  and  colorless,  can  be  flamed 
opaque. 

Carbonic  Acid,  CO2. 

With  Nitric  Acid. — Heat  with  water  and  then  with  dilute 
acid  ;  CO3  will  be  set  free  with  effervescence.  The  escaping 
gas  will  render  lime-water  turbid. 

With  Borax  or  S.  Ph. — After  the  flux  has  been  fused  to  a 
clear  bead,  the  addition  of  a  carbonate  will  cause  effervescence 
during  further  fusion. 

Chlorine,  Cl. 

With  S.  Ph.,  saturated  with  CtiO. — Treated  at  tip  of  blue 
flame  the  bead  will  be  surrounded  by  an  intense  azure-blue 
flame. 

On  Coal,  with  CuO. — Grind  with  a  drop  of  H2SO4 ,  spread 
the  paste  on  coal,  dry  gently  in  O.  F.,  and  treat  with  blue 
flame,  which  will  be  colored  greenish  blue  and  then  azure-blue. 

Chromium,  Cr. 

With  Borax  or  S.  Ph. — O.  F.  Reddish  hot,  fine  yellow  green 
cold. 

R.  F.  In  borax,  green  hot  and  cold.  In  S.  Ph.  red  hot, 
green  cold. 

With  Soda. — O.  F.  Dark  yellow  hot,  opaque  and  light  yellow 
cold. 

R.  F.  Opaque  and  yellowish  green  cold. 

Interfering  Elements. 

Manganese. — The  soda  bead  in  O.  F.  will  be  bright  yellowish 
green. 


PRELIMINARY  EXAMINATION.  2J 

Cobalt,  Co. 

On  Coal,  R.  F. — The  oxide  becomes  magnetic  metal.  The 
solution  in  HC1  will  be  rose-red,  but  on  evaporation  will  be 
blue. 

With  Borax  or  S.  Ph. — Pure  blue  in  either  flame. 

Interfering  Elements. 

Arsenic. — Roast  and  scorify  with  successive  additions  of 
borax.  There  may  be,  in  order  given:  Yellow  (iron),  green 
(iron  and  cobalt),  blue  (cobalt),  reddish  brown  (nickel),  green 
(nickel  and  copper),  blue  (copper). 

Copper  and  other  Elements  which  Color  Strongly. — Fuse  with 
borax  and  lead  on  coal  in  R.  F.  The  borax  on  platinum  wire 
in  O.  F.  will  show  the  cobalt,  except  when  obscured  by  much 
iron  or  chromium. 

Iron,  Nickel,  or  Chromium. — Fuse  in  R.  F.  with  a  little 
metallic  arsenic,  then  treat  as'  an  arsenide. 

Sulphur  or  Selenium. — Roast  and  scorify  with  borax,  as 
before  described. 

Copper,  Cu. 

On  Coal,  R.  F. — Formation  of  red  metallic  metal. 

Flame. — Emerald-green  or  azure-blue,  according  to  com- 
pound. The  azure  -  blue  flame  may  be  obtained  (sulphur, 
selenium,  and  arsenic  should  be  removed  by  roasting ;  lead 
necessitates  a  gentle  heat) — 

(a)  By  moistening  with  HC1  or  aqua  regia,  drying  gently  in 
O.  F.,  and  heating  strongly  in  R.  F. ; 

(b]  By  saturating  S.  Ph.  bead  with  substance,  adding  com- 
mon salt,  and  treating  with  blue  flame. 

With  Borax  or  S.  Ph. — O.  F.  Green  hot,  blue  or  greenish 
blue  cold.  (By  repeated  slow  oxidation  and  reduction,  a  borax 
bead  becomes  ruby-red.) 

R.  F.  Greenish  or  colorless  hot,  opaque  and  brownish  red 
cold.  With  tin  on  coal  this  reaction  is  more  delicate. 


28  A   MANUAL   OF  PRACTICAL  ASSAYING. 

Interfering  Elements. 

General  Method. — Roast  thoroughly,  treat  with  borax  on 
coal  in  strong  R.  F.  (oxides,  sulphides,  sulphates,  are  best 
reduced  by  a  mixture  of  soda  and  borax),  and — 

If  Button  Forms. — Separate  the  button  from  the  slag,  re- 
move any  lead  from  it  by  O.  F.,  and  make  either  S.  Ph.  or 
flame  test  upon  residual  button. 

If  No  Visible  Button  Forms. — Add  test  lead  to  the  borax 
fusion,  continue  the  reduction,  separate  the  button,  and  treat 
as  in  next  test  (lead  alloy). 

Lead  or  Bismuth  Alloys. — Treat  with  frequently  changed 
boracic  acid  in  strong  R.  F.,  noting  the  appearance  of  slag  and 
residual  button. 

Trace. — A  red  spot  in  the  slag. 

Over  One  Per  Cent. — The  residual  button  will  be  bluish 
green ;  when  melted  will  dissolve  in  the  slag  and  color  it  red 
upon  application  of  the  O.  F.,  or  may  be  removed  from  the 
slag  and  be  submitted  to  either  the  S.  Ph.  or  the  flame  test. 

Fluorine,  F. 

Etching  Test. — If  fluorine  be  released  it  will  corrode  glass 
in  cloudy  patches,  and  in  presence  of  silica  there  will  be  a 
deposit  on  the  glass.  According  to  the  refractoriness  of  the 
compound  the  fluorine  may  be  released — 

(a)  In  closed  tube  by  heat ; 

(b)  In  closed  tube  by  heat  and  KHSO4  ; 

(c)  In  open  tube  by  heat  and  glass  of  S.  Ph. 

With  Cone.  H£O<  and  SiOz.—li  heated,  and  the  fumes 
condensed  by  a  drop  of  water  upon  a  platinum  wire,  a  film  of 
silicic  acid  will  form  upon  the  water. 

Iodine,  I. 

With  S.  Ph.,  saturated  with  Cu O.— Treated  at  the  tip  of  the 
blue  flame,  the  bead  is  surrounded  by  an  intense  emerald-green 
flame. 


PRELIMINARY  EXAMINATION.  2$ 

In  Matrass  with  KHSO^. — Violet,  choking  vapor  and  brown 
sublimate. 

In  Open  Tube,  with  equal  parts  Bismuth  Oxide,  Sulphur, 
and  Soda. — A  brick-red  sublimate. 

With  Starch  Paper. — The  vapor  turns  the  paper  dark  purple 

Interfering  Elements. 

Silver. — The  iodide  melts  in  KHSO4  to  a  dark-red  globule, 
yellow  on  cooling,  and  unchanged  by  sunlight. 

Iron,  Fe. 

On  Coal. — R.  F.  Many  compounds  become  magnetic. 
Soda  assists  the  reaction. 

With  Borax. — O.  F.  Yellow  to  red  hot,  colorless  to  yellow 
cold.  (A  slight  yellow  color  can  only  be  attributed  to  iron 
when  there  is  no  decided  color  produced  by  either  flame  in 
highly-charged  beads  of  borax  and  S.  Ph.) 

R.  F.  Bottle-green.     With  tin  on  coal,  violet-green. 

With  S.  Ph. — O.  F.  Yellow  to  red  hot,  greenish  when  cool- 
ing. Colorless  to  yellow  cold. 

R.  F.  Red  hot  and  cold,  greenish  while  cooling. 

State  of  the  Iron. — A  borax-blue  bead  from  CuO  is  made 
red  by  FeO  and  greenish  by  Fe2O3. 

Interfering  Elements. 

Chromium. — Fuse  with  nitrate  and  carbonate  of  soda  on 
platinum,  dissolve  in  water,  and  test  residue  for  iron. 

Cobalt. — By  dilution  the  blue  of  cobalt  in  borax  may  often 
be  lost  before  the  yellow  of  iron. 

Copper. — May  be  removed  from  borax  bead  by  fusion  with 
lead  on  coal  in  R.  F. 

Manganese. — (a)  May  be  faded  from  borax  bead  by  treat- 
ment with  tin  on  coal  in  R.  F. ; 

(b)  May  be  faded  from  S.  Ph.  bead  by  R.  F. 

Nickel. — May  be  faded  from  borax  bead  by  R.  F. 


3O  A    MANUAL    OF  PRACTICAL   ASSAYING. 

Tungsten  or  Titanium. — The  S.  Ph.  bead  in  R.  F.  will  be 
reddish  brown  instead  of  blue  or  violet. 

Uranium. — As  with  chromium. 

Alloys,  Sulphides,  Arsenides,  etc. — Roast,  treat  with  borax 
on  coal  in  R.  F.,  then  treat  borax  in  R.  F.  to  remove  reducible 
metals. 

Lead,  Pb. 

On  Coal. — In  either  flame  is  reduced  to  malleable  metal, 
and  yields  near  the  assay  a  dark  lemon-yellow  coat,  sulphur- 
yellow  cold,  and  bluish  white  at  border.  (The  phosphate 
yields  no  coat  without  the  aid  of  a  flux.) 

With  Bismuth  Flux: — On  Plaster. — Chrome-yellow  coat, 
blackened  by  (NH4)2S. 

On  Coal. — Volatile  yellow  coat,  darker  hot. 

Flame. — Azure-blue. 

With  Borax  or  S.  Ph. — O.  F.  Yellow  hot,  colorless  cold. 
Flames  opaque  yellow. 

R.  F.  Borax  bead  becomes  clear,  S.Ph.  bead  cloudy. 

Interfering  Elements. 

Antimony. — Treat  on  coal  with  boracic  acid,  and  treat  the 
resulting  slag  on  plaster  with  bismuth  flux. 

Arsenic  Sulphide. — Remove  by  gentle  O.  F. 

Cadmium. — Remove  by  R.  F. 

Bismuth. — Usually  the  bismuth-flux  tests  on  plaster  are 
sufficient.  In  addition  the  lead  coat  should  color  the  R.  F. 
blue. 

Lithium,  Li. 

Flame. — Crimson,  best  obtained  by  gently  heating  near  the 
wick. 

Interfering  Elements. 

Sodium. — (a)  Use  a  gentle  flame  and  heat  near  the  wick ; 
(b)  Fuse  on  platinum  wire  with  baric  chloride  in  O.  F.  The 


UNIVERSITY 


PRELIMINARY  EXAMINATION.  3! 

flame  will  be  first  strong  yellow,  then  green,  and,  lastly, 
crimson. 

Calcium,  or  Strontium. — As  these  elements  do  not  color  the 
flame  in  the  presence  of  baric  chloride,  the  above  test  will 
answer. 

Silicon. — Make  into  a  paste  with  boracic-acid  flux  and 
water,  and  fuse  in  the  blue  flame.  Just  after  the  flux  fuses  the 
red  flame  will  appear. 

Magnesium,  Mg. 

On  Coal,  with  Soda. — Insoluble,  and  not  absorbed  by  the 
coal. 

With  Borax  or  S.  Ph. — Clear  and  colorless ;  can  be  flamed 
opaque-white. 

With  Cobalt  Solution. — Strongly  heated,  becomes  a  pale- 
flesh  color.  (With  silicates  this  action  is  of  use  only  in  the 
absence  of  coloring  oxides.  The  phosphate,  arsenate,  and 
borate  become  violet-red.) 

Manganese,  Mn. 

With  Borax  or  S.  Ph. — O.  F.  Amethystine  hot,  reddens  on 
cooling.  With  much,  is  black  and  opaque.  (The  colors  are 
more  intense  with  bdrax  than  with  S.  Ph.)  If  a  hot  bead  is 
touched  to  a  crystal  of  sodic  nitrate  an  amethystine  or  rose- 
colored  froth  is  formed. 

R.  F.  Colorless  or  with  black  spots. 

With  Soda. — O.  F.  Bluish  green  and  opaque  when  cold. 
Sodic  nitrate  assists  the  reaction. 

Interfering  Elements. 

Chromium. — The  soda  bead  in  O.  F.  will  be  bright  yellow- 
ish green  instead  of  bluish  green. 

Silicon. — Dissolve  in  borax,  then  make  soda  fusion. 


32  A   MANUAL    OF  PRACTICAL  ASSAYING. 

Mercury,  Hg. 

With  Bismuth  Flux: — On  Plaster. — Volatile  yellow  and 
scarlet  coat.  If  too  strongly  heated  the  coat  is  black  and 
yellow. 

On  Coal. — Faint-yellow  coat  at  a  distance. 

In  Matrass,  with  Dry  Soda  or  zvith  Litharge. — Mirror-like 
sublimate,  which  may  be  collected  in  globules.  (Gold-leaf  is 
whitened  by  the  slightest  trace  of  vapor  of  mercury.) 

^  f 

Molybdenum,  Mo. 

On  Coal. — O.  F.  A  coat  yellowish  hot,  white  cold  ;  crystal- 
line near  assay. 

R.  F.  The  coat  is  turned  in  part  deep  blue,  in  part  dark 
copper-red. 

Flame. — Yellowish  green. 

With  Borax. — O.  F.  Yellow  hot,  colorless  cold. 

R.  F.  Brown  to  black  and  opaque. 

With  S.  Ph. — O.  F.  Yellowish  green  hot,  colorless  cold. 
(Crushed  between  damp  unglazed  paper  becomes  red,  brown, 
purple,  or  blue,  according  to  amount  present.) 

R.  F.   Emerald-green. 

Dilute  (£)  HCl  Solutions. — If  insoluble,  the  substance  may 
first  be  fused  with  S.  Ph.  in  O.  F.  Then,  if  dissolved  in  the 
acid  and  heated  with  metallic  tin,  zinc,  or  copper,  the  solutions 
will  be  successively  blue,  green,  and  brown.  If  the  S.Ph.  bead 
has  been  treated  in  R.  F.  the  solution  will  become  brown. 

Nickel,  Ni. 

On  Coal,  R.  F. —  The  oxide  becomes  magnetic. 
With  Borax. — O.  F.  Violet  hot,  pale  reddish  brown  cold. 
R.  F.  Cloudy,  and  finally  clear  and  colorless. 
With  S.  Ph.—Q.  F.  Red  hot,  yellow  cold. 
R.  F.  Red  hot,  yellow  cold.      On  coal  with  tin  becomes 
colorless. 


PRELIMINARY  EXAMINATION.  33 

Interfering  Elements. 

General  Method. — Saturate  two  or  three  borax  beads  with 
roasted  substance,  and  treat  on  coal  with  strong  R.  F.  If  a 
visible  button  results,  separate  it  from  the  borax  and  treat 
with  S.  Ph.  in  the  O.  F.,  replacing  the  S.  Ph.  when  a  color  is 
obtained.  If  no  visible  button  results,  add  either  a  small  gold 
button  or  a  few  grains  of  test-lead.  Continue  the  reduction, 
and — 

With  Gold. — Treat  the  gold  alloy  on  coal  with  S.  Ph.  in 
strong  O.  F. 

With  Lead. — Scorify  button  with  boracic  acid  to  small  size, 
complete  the  removal  of  lead  by  O.  F.  on  coal,  and  treat 
residual  button  with  S.  Ph.  in  O.  F. 

Arsenic. — Roast  thoroughly,  treat  with  borax  in  R.  F.  as 
long  as  it  shows  color,  treat  residual  button  with  S.  Ph.  in 
O.  F. 

Alloys. — Roast  and  melt  with  frequently  changed  borax  in 
R.  F.,  adding  a  little  lead  if  infusible.  When  the  borax  is  no 
longer  colored,  treat  the  residual  button  with  S.  Ph.  in  O.  F. 

Nitric  Acid,  HNO3. 

In  Matrass  with  KHSO^ ,  or  in  Closed  Tube  with  Litharge. 
—Brown  fumes  with  characteristic  odor.  The  fumes  will  turn 
ferrous-sulphate  paper  brown. 

Phosphorus,  P. 

Flame. — Greenish  blue,  momentary.  Improved  by  cone. 
H,SO,. 

In  Closed  Tube  ivith  Dry  Soda  and  Magnesium. — The  soda 
and  substance  are  mixed  in  equal  parts  and  dried,  and  made 
to  cover  the  magnesium.  Upon  strongly  heating  there  will  be 
a  vivid  incandescence,  and  the  resulting  mass,  crushed  and 
moistened,  will  yield  the  odor  of  phosphuretted  hydrogen. 

Potassium,  K. 

Flame. — Violet,  except  borates  and  phosphates. 


34  A   MANUAL   OF  PRACTICAL  ASSAYING. 

Interfering  Elements. 

Sodium. — (a)  The  flame  through  blue  glass  will  be  violet  or 
blue; 

(b)  A  bead  of  borax  and  a  little  boracic  acid  made  brown 
by  nickel  will  become  blue  on  addition  of  a  potassium  com- 
pound. 

Lithium. — The  flame  through  green  glass  will  be  bluish 
green. 

Selenium,  Se. 

On  Coaly  R.  F. —  Disagreeable  horse-radish  odor,  brown 
fumes,  and  a  volatile  steel-gray  coat  with  a  red  border. 

In  Open  Tube.  —  Steel-gray  sublimate  with  red  borderr 
sometimes  white  crystals. 

In  Closed  Tube. — Dark-red  sublimate  and  horse-radish  odor, 

Flame. — Azure-blue. 

On  Coaly  with  Soda. — Thoroughly  fuse  in  R.  F.,  place  on 
bright  silver,  moisten,  crush,  and  let  stand.  The  silver  will  be 

blackened. 

t 
Silicon,  Si. 

On  Coal,  with  Soda. — With  its  own  volume  of  soda,  dis- 
solves with  effervescence  to  a  clear  bead.  With  more  soda 
the  bead  is  opaque. 

With  Borax. — Clear  and  colorless. 

With  S.  Ph. — Insoluble.  The  test  made  upon  a  small 
fragment  will  usually  show  a  translucent  mass  of  undissolved 
matter  of  the  shape  of  the  original  fragment. 

When  not  decomposed  by  S.  Ph.,  dissolve  in  borax  nearly 
to  saturation,  add  S.  Ph.,  and  re-heat  for  a  moment.  The 
bead  will  become  milky  or  opaque-white. 

Silver,  Ag. 

On  Coal. — Reduction  to  malleable  white  metal. 

With  Borax  or  S.  Ph.—Q.  F.  Opalescent. 

Cupellation. — Fuse  on  coal  with  one  volume  of  borax-glass 


PRELIMINARY  EXAMINATION.  35 

and  one  to  two  volumes  of  test-lead  in  R.  F.  for  about  two 
minutes.  Remove  button  and  scorify  it  in  R.  F.  with  fresh, 
borax,  then  place  button  on  cupel  and  blow  O.  F.  across  it, 
using  as  strong  blast  and  as  little  flame  as  are  consistent  with 
keeping  button  melted. 

If  the  litharge  is  dark,  or  if  the  button  freezes  before 
brightening,  or  if  it  brightens  but  is  not  spherical,  rescorify  it 
on  coal  with  borax,  add  more  test-lead,  and  again  cupel,  until 
there  remains  only  a  white  spherical  button  of  silver. 

Sodium,  Na. 
Flame. — Reddish  yellow. 

Strontium,  Sr. 

On  Coal,  with  Soda. — Insoluble,  absorbed  by  the  coal. 

Flame. — Intense  crimson,  improved  by  moistening  with 
HC1. 

With  Borax  or  S.  Ph. — Clear  and  colorless ;  can  be  flamed 
opaque. 

Interfering  Elements. 

Barium. — The  red  flame  may  show  upon  first  introduction 
of  the  sample  into  the  flame,  but  it  is  afterwards  turned  brown- 
ish yellow. 

Lithium. — Fuse  with  baric  chloride,  by  which  the  lithium 
flame  is  unchanged. 

Sulphur,  So 

On  Coal,  with  Soda  and  a  little  Borax. — Thoroughly  fuse  in 
the  R.  F.  flame,  and  either, 

(a)  Place  on  bright  silver,  moisten,  crush,  and    let  stand. 
The  silver  will  become  brown  or  black.     Or, 

(b)  Heat  with  dilute  HC1  (sometimes  with  powdered  zinc); 
the  odor  of  H2S  will  be  observed. 

In  Open  Tube. — Suffocating  fumes.  Some  sulphates  are 
unaffected. 


36  A   MANUAL   OF  PRACTICAL   ASSAYING. 

In  Closed  Tube. — May  have  sublimate  red  when  hot,  yellow 
cold,  or  sublimate  of  undecomposed  sulphide,  or  the  substance 
may  be  unaffected. 

With  Soda  and  Silica  (equal  parts). — A  yellow  or  red  bead. 

To  Determine  whether  Sulphide  or  Sulphate. — Fuse  with 
6oda  on  platinum  foil.  The  sulphide  only  will  stain  silver. 

Tellurium,  Te. 

On  Coal. — Volatile  white  coat  with  red  or  yellow  border. 
If  the  fumes  are  caught  on  porcelain,  the  resulting  gray  or 
brown  film  may  be  turned  crimson  when  moistened  with  cone. 
H3SO4 ,  and  gently  heated. 

On  Coalj  with  Soda. — Thoroughly  fuse  in  R.  F.  Place  on 
bright  silver,  moisten,  crush,  and  let  stand.  The  silver  will  be 
blackened. 

Flame. — Green. 

In  Open  Tube. — Gray  sublimate  fusible  to  clear  drops. 

With  H^SOt  (cone.). — Boiled  a  moment,  there  results  a  pur- 
ple-violet solution,  which  loses  color  on  further  heating  or  on 
dilution. 

Tin,  Sn. 

On  Coal. — O.  F.  The  oxide  becomes  yellow  and  lumirous. 

R.  F.  A  slight  coat,  assisted  by  additions  of  sulphur  or  soda. 

With  Cobalt  Solution. — Moisten  the  coal  in  front  of  the 
assay,  with  the  solution,  and  blow  a  strong  R.  F.  upon  the 
assay.  The  coat  will  be  bluish  green  when  cold. 

With  CuO  in  Borax  Bead. — A  faint-blue  bead  is  made 
reddish  brown  or  ruby-red  by  heating  a  moment  in  R.  F.  with 
a  tin  compound. 

Interfering  Elements. 

Lead  or  Bismuth  Alloys. — It  is  fair  proof  of  tin  if  such  an 
alloy  oxidizes  rapidly  with  sprouting  and  cannot  be  kept  fused. 

Zinc. — On  coal  with  soda,  borax,  and  charcoal  in  R.  F.,  the 
tin  will  be  reduced,  the  zinc  volatilized ;  the  tin  may  then  be 
washed  from  the  fused  mass. 


PRELIMINARY  EXAMINATION.  37 

Titanium,  Ti. 

With  Borax. — O.  F.  Colorless  to  yellow  hot,  colorless  cold, 
opalescent  or  opaque  white  by  flaming. 

R.  F.  Yellow  to  brown,  enamel-blue  by  flaming. 

With  Ph.  S.— O.  F.  as  with  borax. 

R.  F.  yellow  hot,  violet  cold. 

HCl  Solutions. — If  insoluble,  the  substance  may  first  be 
fused  with  S.  Ph.  or  with  soda,  and  reduced.  If  then  dissolved 
in  dilute  acid  and  heated  with  metallic  tin,  the  solution  will 
become  violet  after  standing.  Usually  there  will  also  be  a  turbid 
violet  precipitate,  which  becomes  white. 

Interfering  Elements. 

Iron. — The  S.  Ph.  bead  in  R.  F.  is  yellow  hot,  brownish 
red  cold. 

Tungsten,  W. 

With  Borax. — O.  F.  Flame  colorless  to  yellow  hot,  colorless 
cold  ;  can  be  flamed  opaque  white. 

R.  F.  Colorless  to  yellow  hot,  yellowish  brown  cold. 

With  S.  Ph.—O.  F.  Clear  and  colorless. 

R.  F.  Greenish  hot,  blue  cold.  On  long  blowing  or  with 
tin  on  coal  becomes  dark  green. 

With  Dilute  HCl. — If  insoluble,  the  substance  may  first  be 
fused  with  S.  Ph.  The  solution  heated  with  tin  becomes  dark 
blue  ;  with  zinc  it  becomes  purple  and  then  reddish  brown. 

Interfering  Elements. 
Iron. — The  S.  Ph.  in  R.  F.  is  yellow  hot,  blood-red  cold. 

Uranium,  U. 

With  Borax. — O.  F.  Yellow  hot,  colorless  cold  ;  can  be 
flamed  enamel-yellow. 

R.  F.  Bottle-green  ;  can  be  flamed  black,  but  not  enamelled. 


38  A    MANUAL   OF  PRACTICAL   ASSAYING. 

With  S.  P/i.—O.  F.  Yellow  hot,  yellowish  green  cold. 
R.  F.   Emerald-green. 

Interfering  Elements. 
Jron.—With  S.  Ph.  in  R.  F.  is  green  hot,  red  cold. 

Vanadium,  V. 

With  Borax. — O.  F.  Colorless  or  yellow  hot,  greenish-yel- 
low cold. 

R.  F.  Brownish  hot,  emerald-green  gold. 

With  S.  /%.— O.  F.   Dark  yellow  hot,  light  yellow  cold. 

R.  F.  Brown  hot,  emerald-green  cold. 

//,S6>4  Solutions. — Reduced  by  zinc  becomes  successively 
yellow,  green,  bluish-green,  blue,  greenish-blue,  bluish-violet, 
and  lavender. 

Zinc,  Zn. 

On  Coal. — O.  F.  The  oxide  becomes  yellow  and  luminous. 

R.  F.  Yellow  coat,  white  when  cold,  assisted  by  soda  and 
a  little  borax. 

With  Cobalt  Solution. — Moisten  the  coal  in  front  of  the 
assay,  with  the  solution,  and  blow  a  strong  R.  F.  upon  the 
assay.  The  coat  will  be  bright  yellow-green  when  cold. 

Interfering  Elements. 

Antimony. — Remove  by  strong  O.  F.,  or  by  heating  with 
sulphur  in  closed  tube. 

Cadmium,  Lead,  or  Bismuth. — The  combined  coats  will  not 
prevent  the  cobalt-solution  test. 

Tin. — The  coats  heated  in  an  open  tube,  with  charcoal  dust 
by  the  O.  F.,  may  yield  white  sublimate  of  zinc. 

QUALITATIVE  TESTS. 

The  following  summary  of  characteristic  qualitative  tests  in 
the  wet  way  will  be  found  useful  in  the  preliminary  examina- 
tion of  ores,  furnace  products,  etc. : 


PRELIMINARY  EXAMINATION.  39 

Aluminium,  Al. 

1.  Alkali    hydroxides  precipitate  grayish-white,  Ala(HO)6, 
soluble  in  fixed  alkali-hydroxides,  but  only  slightly  soluble  in 
NH4OH  if  NH4C1  is  present. 

2.  Basic  acetate  of  aluminium  is  precipitated  by  addition  of 
NaC8H3Oa  to  a  warm  and  slightly  acid  solution. 

Confirm. — By  blowpipe  test. 

Antimony,  Sb. 

1.  HaS  precipitates  orange-red  SbaS3  from  acid  solutions. 
The  precipitate  is  soluble  in  HC1,  in  alkalies,  and  in  alkaline 
sulphides. 

2.  HaS  precipitates  orange  Sb2S5  from  acid  solutions.     The 
precipitate  is  soluble  in  HC1,  in  alkalies,  and  alkaline  sulphides. 

To  distinguish  between  SbaO3  and  SbaO6,  add  solution  of 
AgNO3,  in  the  presence  of  KOH  or  NaOH.  S£a<93  precipi- 
tates black,  Ag4O,  which  is  insoluble  in  NH4OH  ;  and  S£a<96 
precipitates  white,  AgSbO3,  which  is  soluble  in  NH4OH. 

Arsenic,  As. 

1.  HaS  precipitates  yellow  AsaS3  best  from  HC1  solutions. 
Soluble  in  alkalies  and  alkaline  sulphides,  insoluble  in  HC1. 

2.  HaS  precipitates  yellow,  As2S5  from  acid  solutions  after 
heating  solution  and  passing  gas  for  some  time. 

3.  AgNO3    precipitates  yellow  Ag3AsO3  or   reddish-brown 
Ag3AsO4,  soluble  in  dilute  acids,  ammonia,  and  ammonia  salts. 

4.  CuSO4  precipitates  yellowish-green  Cu3(AsO3)a  or  green- 
ish-blue,  CuHAsO4,  soluble  in  NH4OH  and  NH4C1. 

5.  Ammonium  magnesia  mixture  precipitates  white  MgNH4 
As04. 

Barium,  Ba. 

I.  Alkali  carbonates  precipitate  white  BaCOs  soluble  in 
HC1  and  HNO3 .  Soluble  in  acids. 


40  A   MANUAL    OF  PRACTICAL  ASSAYING. 

2.  Soluble  sulphates  and   HaSO4  precipitate  white  BaSO4, 
which  is  practically  insoluble  in  acids  and  water. 
Confirm.  —  By  blowpipe  test. 

Bismuth,  Bi. 

1.  HaS  or  (NH4)2S  precipitates  brownish-black  BiaS3  insolu- 
ble in  dilute  acids,  but  soluble  in  strong  HNO3. 

2.  H2O    precipitates  from    the    chloride    white   BiOCl,  in- 
soluble in  an  excess,  but  soluble  in  HC1  and  HNO3. 

3.  SnCla  in  the  presence    of  NaOH  or  KOH  precipitates 

6fea*Bi,Ot- 

Confirm. — By  blowpipe  test. 

Bromine,  Br. 

I.  AgNO3  precipitates  yellowish-white  AgBr ;  changes  ta 
gray,  soluble  in  KCN,  slightly  soluble  in  NH4OH,  insoluble  in 
HNOS. 

Separation  of  Cl,  Br,  and  L — Place  a  solution  of  the  mixture 
in  a  test-tube  with  a  little  MnO2  and  water,  add  a  drop  of  dilute 
H2SO4  (one  in  ten).  A  brown  color  indicates  I.  Boil ;  violet 
vapors  are  given  off.  When  these  cease  add  2  cc.  of  H2SO4 
and  boil ;  brown  vapors  indicate  Br.  Boil  until  brown  vapors 
cease  and  cool.  When  cold,  add  an  equal  volume  of  H2SO4 
and  heat ;  green  vapors  indicate  Cl. 

Boron,  B. 

1.  Bad,  and  CaCla  precipitate  white  Ba3(BOs)a  and  Cas(BO3)a. 

2.  AgNO3  precipitates  white  Ag3BO3. 

3.  Free  boracic   acid   turns  turmeric   paper  brownish  red, 
becoming  more  intense  when  the  paper  is  dried.    When  mixed 
with  HC1  to  acid  reaction  and  dried  it  becomes  red. 

Cadmium,  Cd. 

I.  HaS  or  (NH4)2S  precipitates  yellow  CdS,  insoluble  in 
dilute  acids,  alkalies,  alkali  sulphides,  or  cyanides.  Soluble  iu 
strong  hot  HC1,  HNO3,  and  H2SO4. 


PRELIMINARY  EXAMINATION.  4! 

2.  Zn   precipitates    from   acid    and   ammoniacal   solutions 
gray  Cd. 

3.  KOH  and  NaOH  precipitate  white  Cd(OH)2 ,  insoluble 
in  excess;  whilst  NH4OH  precipitate  white  Cd(OH)2,  which  is 
soluble  in  excess. 

Confirm. — By  blowpipe  test. 

Calcium,  Ca. 

1.  H2SO4  precipitates  white  CaSO4 ,  soluble  in  a  concentrated 
solution  of  (NH4)2SO4 ;  distinction  from  Ba  and  Sr. 

2.  Alkaline  arseniates  precipitate  CaH  AsO3 ,  soluble  in  acids 
and   NH4OH.     Ba,  Sr,  and   Mg  give  this  precipitate  only  in 
concentrated  solutions.     Ammonia  salts  must  be  absent. 

Confirm. — By  blowpipe  test. 

Carbonic  Acid,  CO2. 

I.  Add  HNO3  to  substance  in  a  test-tube,  and  pass  gas 
through  a  solution  of  lime-water.  A  white  precipitate  of  CaCGs 
indicates  CO2. 

Chlorine,  Cl. 

I.  AgNO3  precipitates  white  AgCl,  soluble  in  NH4OH. 

Chromium,  Cr. 

1.  NH4OH    precipitates    bluish  green   Cr2(OH)6 ,    slightly 
soluble  in  excess. 

2.  From    solutions   of    CrO3  lead    salts    precipitate  yellow 
PbCrO4,  soluble  in    HNO3  and  insoluble  in  acetic  acid.     Diffi- 
cultly soluble  in  KOH. 

3.  A  very  delicate  test  for  Cr  as  CrO3  is  by  means  of  H.2O^ 
(hydrogen  peroxide)  and  ether,  giving  a  fine  blue  color. 

Cobalt,  Co. 

I.  Fixed  alkalies  precipitate  blue  basic  salts.  This  precipi- 
tate absorbs  oxygen  and  becomes  olive-green  hydroxide.  If 


UNIVERSITY 


42  A    MANUAL    OF  PRACTICAL   ASSAYING. 

boiled  before  oxidation  in  the"  air  becomes  rose-red  Co(OH)2; 
does  not  dissolve  in  excess.  HN4OH  produces  the  same 
precipitate,  which  is  soluble  in  excess. 

2.  K3FeCeN6  precipitates  dark  brown  Co3(FeC6N6)2 ,  insolu- 
ble in  HC1.     If  to  a  solution  of  Co  or  Ni  an  excess  of  NH4C1 
and  NH4OH  is  added  and  then  K3FeC6N6,  a  blood-red  color 
indicates  Co.     If  Ni  is  present,  and  the  solution  is  boiled,  a 
copper-red  precipitate  forms  ;  if  any  Co  is  present,  a  dirty  green, 
on  boiling. 

3.  To  a  dilute  solution  of  cobaltous  nitrate  add  tartaric  or 
citric  acid,  then  an   excess  of  ammonia,  and  a  few  drops  of 
potassium  ferricyanide  ;  a  deep-red  color  appears,  even  if  largely 
diluted. 

Confirm. — By  blowpipe  test. 

Copper,  Cu. 

1.  NH4OH  produces  a  deep-blue  solution. 

2.  NaOH  and  KOH  when  added  to  saturation  precipitate 
Itlue  Cu(OH)2,  insoluble  in  excess.     When  boiled  the  precipi- 
tate changes  to  black  Cu3O2(OH)2.     Organic  substances  gen- 
erally prevent  the  formation  of  this  precipitate. 

3.  Fe   and   Zn   precipitate   metallic   copper   from   cupric 
solutions. 

Iron,  Fe. 

FeO.—i.  K3FeC6N8  precipitates  dark-blue  Fe3(FeC6N6)3 ,  in- 
soluble in  acids. 

2.  NH4OH  precipitates  white  Fe(OH)3. 

Fe^Oy — I.  NH4CNS  produces  a  blood-red  solution,, 

2.  NH4OH  precipitates  brownish  Fea(OH)6. 

Lead,  Pb. 

1.  Zn  precipitates  crystals  of  Pb. 

2.  H2SO4  precipitates  white  PbSO4 ,  slightly  soluble  in  ex- 
cess, insoluble  in  alcohol,  but  soluble  in  ammonium  acetate  or 
•citrate. 


PRELIMINARY  EXAMINATION.  43 

3.  H2S  or  (NH4)2S  precipitates  black  PbS,  soluble  in  HNO. 
with  formation  of  PbSO4. 

4.  K4FeC6N8  precipitates  white  PbaFeC6N6. 

Lithium,  Li. 

1.  Nitrophenic  acid  forms  a  yellow  precipitate. 

2.  Na2CO3   precipitates  white  LiaCO3 ,   slightly  soluble  in 
HS0. 

Confirm. — By  blowpipe  and  spectroscope. 

Magnesium,  Mg. 

I.    Na2HPO4    precipitates,    in    presence    of    NH4OH    and 
NH4C1,  white  MgNH4PO4.     Fine  crystals. 
Confirm. — By  blowpipe. 

Manganese,  Mn. 

1.  Boil  with  HNO3,  and  add  peroxide  of  lead.     A  reddish- 
vtolet  solution  (color  of  potassium  permanganate)  indicates  Mn. 

Mercury,  Hg. 

:.    A  piece  of   bright    metallic   copper   is    coated   with    a 
precipitate  of  metallic  Hg,  upon  insertion  in  a  solution  of  Hg. 

2.  SnCl2  precipitates  first  white  Hg2Cl2  and  then  gray  Hg. 
To  distinguish  between  mercurous  and  mercuric  compounds 

HC1  precipitates  white  Hg2Cl2 ,  soluble  in  aqua  regia,  HNO3 ,  and 
NH4C1,  and  blackened  by  NH4OH,  from  mercurous  compounds. 
No  precipitate  on  addition  of  HC1  to  mercuric  compounds. 

Molybdenum,  Mo. 

Upon  heating  the  acid  solution  with  metallic  zinc  it  will  turn 
successively  blue,  green,  and  brown. 
Confirm. — By  blowpipe  test. 

Nickel,  Ni. 

I.    Alkaline   carbonates   precipitate   green   basic  carbonate 
2NiCO3,  3Ni(OH),,  soluble  in  (NH4)aCO3  or,  in  excess  of  re- 


44  A    MANUAL    OF  PRACTICAL   ASSAYING. 

agent,  with  blue  or  greenish-blue  color.     Again  precipitated  by 
KOH  or  NaOH  *s  pale-green  Ni(OH)2. 

2.  NH4OH  in  excess  gives  blue  color. 

3.  KCN  precipitates  pale-green  NiC2N2,  soluble  in  excess. 
Upon    boiling   with    NaCIO,    black    Ni(OH)3    is   precipitated. 
Distinction  from  Co,  which  gives  a  dirty-zvhite  precipitate  with 
KCN,  soluble  in  excess,  but  no  precipitate  being  formed  on 
boiling  with  NaCIO. 

Nitric  Acid,  HNO3. 

1.  To  the  solution,  in  a  test-tube,  add  a  saturated  solution 
of  ferrous  sulphate,  and  then  concentrated  sulphuric  acid  (free 
from  HNO3);  a  brown  ring  between   the  FeSO4  and  H2SO4 
indicates  HNO3. 

Phosphorus,  P. 

Orthophosphates. — I.  Magnesia  mixture  precipitates  white 
MgNH4P04. 

2.  AgNO3  precipitates  light-yellow  Ag3PO4,  soluble  in  HNOS 
and  NH4OH. 

3.  (NH  )2MoO4+  HNO3  precipitatesj^//0z£>  ammonium  phos- 
pho-molybdate  ;  composition  variable.     The  precipitate  is  sol- 
uble in  NH4OH,  in  excess  of  phosphoric  acid,  and  is  prevented 
by  organic  substances,  such  as  tartaric  acid. 

Pyrophosphates. —  i.  MgSO4  precipitates  white  Mg2P2O7  > 
soluble  in  an  excess  of  either  solution.  NH4OH  fails  to  pre- 
cipitate it  from  these  solutions.  On  boiling  it  separates  again. 
By  this  reaction  pyro  can  be  detected  in  the  presence  of  phos- 
phoric acid. 

2.  (NH4)2MoO4  +  HNO3  does  not  give  a  precipitate  until 
orthophosphate  is  formed.     Most   of   the  pyrophosphates  of 
the  heavy  metals  (Ag  an  exception)  are  soluble  in  alkali  pyro- 
phosphates (distinction  from  Orthophosphates). 

3.  AgNO,  precipitates  white  Ag4P3O7 ,  soluble  in  HNOa 
and  NH4OH.     Addition  of  an  alkali  aids  the  precipitation. 

Mctaphosphoric  Acid. — I.  Magnesia  mixture  gives  no  pre- 
cipitate. 


PRELIMINARY  EXAMINATION.  45 

2.  (NH4)2MoO4  -f-  HNO3  gives  no  precipitate. 

3.  AgNO3  precipitates  white  AgPO3 ,  soluble  in  alkali  meta- 
phosphate  solutions  (distinction  from  pyrophosphates). 

4.  Albumen  gives  a  precipitate  (distinction  from  ortho  and 
pyrophosphates). 

5.  Fusion  with  NaaCOa  converts  meta  and  pyro  into  ortho- 
ohosphates. 

Potassium,  K. 

I.  PtCl4  with  HC1  precipitates  yellow  crystalline  (KCl)2PtCl4. 
Evaporate  to  dryness.  The  precipitate  is  not  dissolved  by 
alcohol. 

Confirm. — By  blowpipe  and  spectroscope. 

Selenium,  Se. 

1.  H2S  precipitates  yellow  sulphide  of  selenium,  soluble  in 
<NH4)2S.     Upon  heating  the  precipitate  turns  reddish  yellow. 

2.  SnCl2-|-HCl  produces  a  red  precipitate  of  Se,  which 
turns  gray  at  a  high  temperature. 

3.  Metallic  copper,   when  placed   in   a  warm  solution   of 
selenious   acid,   containing   HC1,   becomes   black;   if  the   fluid 
remains  long  in  contact  with  the  copper,  it  turns  bright  red 
from  separation  of  selenium. 

Confirm. — By  blowpipe  tests. 

Silicon,  Si. 

Silicates  are  determined  by  the  separation  of  SiO2.  Fuse 
With  Na2CO3  +  NaNO3 ,  dissolve  in  HC1,  and  evaporate  to 
dryness.  Upon  evaporation  gelatinous  silica  will  separate  out. 
Upon  heating  and  dissolving  with  HC1  insoluble  SiOa  remains 
behind. 

Confirm. — By  blowpipe  test. 

Silver,  Ag. 

i.  HC1  precipitates  white  AgCl,  insoluble  in  HNO3,  soluble 
in  NH4OH. 


46  A   MANUAL   OF  PRACTICAL  ASSAYING. 

2.  Cu  precipitates  metallic  Ag. 

3.  KI  precipitates  yellow  Agl,  insoluble  in  NH4OH,  soluble 
in  excess  of  reagent. 

Confirm. — By  blowpipe  test. 

Sodium,  Na. 

1.  (NaCl)2PtCl4  crystallizes  from  its  concentrated  solutions 
in  red  prisms. 

2.  KSbO3   (in    neutral   or   alkaline    solutions)   precipitates 
white  NaSbO,.     The  reagent  should  be  dissolved  as  wanted,  as 
it  is  unstable  in  solution. 

Confirm. — By  blowpipe  and  spectroscope. 

Strontium,  Sr. 

i.  NaOH,NH4OH,Na2CO3,(NH4)2CO9,and  NaaHPO4form 
precipitates  which  closely  resemble  those  produced  by  these 
reagents  with  Ba  salts. 

Confirm. — By  blowpipe  tests. 

Sulphur,  S. 

1.  Bad,  gives  a  white  precipitate,  BaSO4 ,  when  added  to 
sulphuric-acid  solutions.    /Practically  insoluble. 

2.  On  addition  of  HNO3  to  sulphides  H2S  is  given  off. 

Tellurium,  Te. 

1.  H,S  precipitates  brown  TeS2  from  acid  solutions.     Sol- 
uble in  (NH4)3S. 

2.  Boiled  with  concentrated   H2SO4  there  results  a  purple- 
violet  solution,  which  fades  upon  further  heating  or  dilution. 

Confirm. — By  blowpipe  tests. 

Tin,  Sn. 

Stannous  Oxide  (SnO). — i.  H2S  precipitates  dark-brown  SnS, 
soluble  in  HC1,  in  alkalies ;  moderately  soluble  in  yellow 
(NH.),S. 


PRELIMINARY  EXAMINATION.  47 


2.  HgCL,  precipitates  white  Hg2Cl2  ,  with  excess  black 
(distinction  from  stannic  compounds). 

3.  AuCl3  with  free  HC1  or  HNO3  ,  a  purple  precipitate. 

4.  Zn  precipitates  spongy  Sn. 
Stannic  oxide  (SnO2). 

1.  H2S  precipitates  yellow  SnSa,  soluble  in  HC1,  in  alkalies. 
and  alkaline  sulphides. 

2.  HgCl2  no  precipitate. 

3.  AuCls  no  precipitate. 

4.  Zn  precipitates  spongy  Sn. 
Confirm.  —  By  blowpipe  tests. 

Titanium,  Ti. 

1.  NH4OH  gives  a  bulky  white  precipitate,  Ti(OH)4,  insol- 
uble in  excess. 

2.  Sn  or  Zn  boiled  in  acid  solutions  after  some  time  give 
pale-violet  or  blue  solutions,   subsequently  a   blue   precipitate, 
which  gradually  becomes  white. 

Confirm.  —  By  blowpipe. 

Tungsten,  W. 

1.  SnCl2  produces  a  yellow  precipitate  on  acidifying  with 
HC1,  and  applying  heat  the  precipitate  acquires  a  beautiful 
blue  color. 

2.  Heated  with  HC1  and  Zn  the  solution  becomes  purple, 
and  then  reddish  brown. 

3.  K4FeC6N6  -f-  HC1  gives  a  deep  brownish-red  color;  after 
some  time  a  precipitate  of  the  same  color  is  produced. 

Uranium,  U. 

1.  NH4OH,  KOH,  and  NaOH  produce  a  yellow  precipitate 
of  uranic  hydroxide  and  alkali. 

2.  K4FeC6N6  produces  a  reddish-brown  precipitate. 
Confirm.  —  By  blowpipe  test. 


48  A    MANUAL    OF  PRACTICAL   ASSAYING. 

Vanadium,  V. 

1.  K4FeC6N6  produces  a  green  flocculent  precipitate,  insol- 
uble in  acids. 

2.  Dissolved  in  H2SO4  and  Zn  added  the  solution  becomes 
successively  green,  blue,  bluish  violet,  and  lavender. 

3.  An  acidified  solution  of  vanadates  upon   being  shaken 
with  hydrogen  dioxide  acquires  a  red  tint ;  if  ether  is  then 
added,  and  the  solution  shaken,  its  retains  its  color,  the  ether 
remaining  colorless. 

Zinc,  Zn. 

1.  Alkali  hydroxides  precipitate  white  Zn(OH)2 ,  soluble  in 
excess  of  precipitant. 

2.  H3S  precipitates  (from  neutral  or  acetic  acid  solutions) 
white  ZnS. 

3.  K4FeC6N6  precipitates  white  Zn3FeC6N6,   insoluble  in 
very  dilute  solutions  of  HC1. 

4.  (NH4)aS  precipitates  white  ZnS,  insoluble  in  KOH  and 
HC.H.O,.  ' 

Confirm. — By  blowpipe  test. 


CHAPTER   IV. 
APPARATUS   AND   OPERATIONS. 

THE  general  apparatus  used  in  the  ordinary  course  of  an 
analysis  or  assay  is  all  that  will  be  discussed  here.  The 
special  pieces  of  apparatus,  such  as  the  apparatus  used  in  the 
analysis  of  gases,  will  be  discussed  under  the  heacl  of  the 
different  determinations. 

Crushing  and  Pulverizing. — A  small  hand-crusher,  or  a 
small  power-crusher,  where  power  can  be  obtained,  will  be 
found  very  convenient  for  crushing  small  samples  of  ore,  slag, 
etc.  If  such  a  crusher  is  not  at  hand,  the  crushing  can  be 
done  in  an  iron  mortar ;  but  in  a  laboratory  where  much  work 
is  done  a  small  jaw-crusher  will  save  a  great  deal  of  time  and 
labor. 

A  cast-iron  bucking-plate  and  muller  are  indispensable  for 
fine  pulverization  of  ore  samples.  The  ordinary  plate  is 
2X2  feet  and  I  inch  thick,  cast  with  flanges  about  I  inch  high 
on  the  two  sides.  The  surface  should  be  planed  perfectly 
smooth.  The  muller  or  grinder  is  of  cast  iron,  about  6  inches 
long,  4  inches  wide,  i%  inches  thick  in  the  middle  and  I  inch 
thick  at  the  two  ends,  so  that  the  surface  is  convex.  The  sur- 
face should  be  planed  smooth  and  true  at, all  points. 

The  crushed  ore  is  spread  upon  the  plate,  a  few  ounces  at 
-a  time,  the  left  hand  being  placed  on  the  muller  so  as  to  throw 
the  weight  of  the  body  on  it,  whilst  the  right  hand  grasps  the 
handle.  The  muller  is  moved  back  and  forth,  depressing  the 
handle  as  it  is  brought  forward  and  raising  it  when  pushing 
the  muller  back. 

A  small  agate  mortar  and  pestle  will  be  found  indispen- 

49 


5O  A   MANUAL   OF  PRACTICAL  ASSAYING. 

sable,  where  wet  determinations  are  to  be  made,  for  finely  pul- 
verizing ores,  etc.,  which  are  decomposed  with  difficulty.  As 
the  pulverizing  in  the  mortar  is  a  tedious  operation,  a  quantity 
of  the  substance  only  slightly  in  excess  of  the  amount  requited 
for  analysis  should  be  taken.  Of  course  this  small  sample 
should  be  carefully  taken  from  the  general  pulverized  sample, 
so  that  it  accurately  represents  the  whole. 

Screening. — After  the  sample  is  cut  down  and  pulverized 
on  the  bucking-plate  it  should  be  passed  through  a  screen  or 
sieve.  What  refuses  to  pass  through  the  sieve  is  again  bucked 
and  screened  until  all  has  passed  through.  The  usual  sieve  is 
one  of  80  or  100  meshes.  This  is  sufficiently  fine  for  samples 
which  arc  to  be  assayed  by  fire-assay,  but  samples  which  are 
to  be  treated  in  the  wet  way  will  frequently  have  to  be  still. 
further  pulverized  in  the  agate  mortar.  The  sieves  come  in 
nests  comprising  20,  40,  60,  80,  and  100  meshes,  each  nest  being 
provided  with  a  tin  box  and  cover.  Such  a  nest  of  sieves  will 
be  found  very  convenient  and  useful  in  a  laboratory  doing 
metallurgical  work. 

Storing  Samples. — Small  paper  sacks,  or,  preferably,  en- 
velopes made  of  heavy  brown  paper  and  provided  with  patent 
end-fasteners,  are  very  convenient  for  keeping  the  pulverized 
samples.  Small  wide-necked  sample-bottles  holding  about 
four  ounces  each  are  sometimes  used  for  this  purpose.  All 
samples  should  be  properly  labelled  and  filed  away  for  a 
reasonable  length  of  time. 

Moulds. — Cast-iron  ingot  moulds  for  casting  bars  of  base 
bullion  or  silver  bullion  will  be  necessary  whe-re  assays  of 
bullion  or  alloys  are  to  be  made. 

Cupel-moulds  and  pestles  are  required  for  making  cupels. 
They  are  made  of  both  brass  and  steel,  the  brass  moulds 
being  preferable.  They  come  in  different  sizes,  those  most 
used  being  moulds  which  will  make  cupels  weighing  about  8 
grammes  and  18  grammes,  respectively. 

Moulds  for  pouring  scorification  and  crucible  charges  are 
necessary.  These  should  be  of  cast-iron,  the  depression  being 
conical  in  shape,  with  the  apex  of  the  cone  slightly  rounded 


APPARATUS  AND   OPERATIONS.  5  I 

off.  They  should  be  of  two  sizes,  the  smaller  for  scorification 
and  the  larger  for  crucible  assays. 

Rolls.— A  set  of  small  steel  hand-rolls  for  flattening  out 
samples  of  gold  and  silver  bullion,  and  gold  cornets  in  the 
gold-bullion  assay,  will  be  found  convenient. 

Weighing. — For  a  laboratory  doing  general  work  (both 
wet  and  dry  assays)  five  balances  will  be  found  useful.  Each 
of  these  balances  should  be  provided  with  the  proper  set  of 
weights.  It  is  best  to  have  separate  weights  for  each  balance. 

A.  A  rough  scales  for  weighing  large  samples  of  ore,  metals, 
etc.     An  ordinary  grocers'  scales   answers   very  well  for  this 
purpose.     This  balance  should  be  provided  with  avoirdupois 
weights. 

B.  A    pulp-balance    for   weighing   out    ore    for   fire-assay. 
This  balance  should  take  120  grammes  in  each  pan,  and  should 
be  sensitive  to  within  5  milligrammes.     It  should  be  provided 
with  a  set  of  gramme  weights   from   5   mgs.  to  20  gms.     It 
should  also  be  provided  with  a  set  of  assay-ton  weights  from 
0.05  A.  T.  to  4  A.  T. 

The  system  of  assay-ton  weights  was  devised  by  Prof. 
C.  F.  Chandler,  of  Columbia  College.  These  weights  are  not 
only  very  convenient,  but  their  use  results  in  the  saving  of 
considerable  time  in  the  calculation  of  the  results  of  gold  and 
silver  assays.  As  ores  of  the  precious  metals,  as  well  as  those 
of  the  base  metals,  are  weighed  in  pounds  avoirdupois,  whilst 
gold  and  silver  are  weighed  in  ounces  Troy,  the  basis  of  the 
system  is  the  number  of  Troy  ounces  in  one  ton  avoirdupois 
(2000  pounds),  which  is  29,166.66  ounces.  The  assay-ton  con. 
tains  29,166.66  milligrammes;  hence  if  one  assay-ton  of  ore  is 
taken  for  assay  and  a  silver  button  weighing  100  milligrammes 
is  obtained,  the  ore  will  assay  100  ounces  of  silver  per  ton,  as 
each  milligramme  in  I  assay-ton  is  equivalent  to  I  ounce  Troy 
per  ton  avoirdupois.  If  f  assay-ton  were  taken  for  assay,  it 
would  be  necessary  to  multiply  the  result  (in  milligrammes)  by 
2  to  obtain  the  assay  value,  etc. 

C.  An   analytical   balance  for  weighing  out  ore,  etc.,   for 
analysis  and  weighing  the  results  of  wet  determinations.    This 


$2  A    MANUAL   OF  PRACTICAL   ASSAYING. 

balance  is  also  used  for  weighing  out  ore  for  scorification-assay 
in  the  case  of  rich  ores  and  the  buttons  obtained  by  fire-assay 
for  base  metals.  The  balance  should  take  at  least  30  grammes 
in  each  pan,  and  should  be  sensitive  to  within  0.5  milligramme. 
It  should  be  enclosed  in  a  glass  case,  and  should  be  kept  free 
from  moisture,  fumes,  etc.  It  should  be  provided  with  a  set 
of  gramme  weights  from  i.o  mgm.  to  30  gms.,  and  also  with 
a  beam-rider  for  weighing  milligrammes  and  fractions  of  milli- 
grammes. The  best  balances  are  provided  with  agate  knife- 
edges. 

•-. £,D.  A  button-balance,  for  weighing  the  gold  and  silver 
beads  and  for  weighing  out  samples  of  gold  and  silver  bullion 
for  assay.  This  balance  should  take  at  least  I  gm.  in  each  pan, 
and  should  be  sensitive  to  within  ^L-  mgm.  It  should  be  pro- 
vided with  a  set  of  gramme  weights  from  i  mgm.  to  I  gm.,  and 
a  beam-rider  for  weighing  fractions  of  a  milligramme.  It  should 
be  provided  with  a  glass  case  and  agate  knife-edges,  and  should 
be  kept  free  from  dust,  fumes,  etc.  The  balance  should  not 
be  exposed  to  the  direct  rays  of  the  sun,  as  they  cause  expan- 
sion of  the  metal-work  and  throw  it  out  of  balance. 

E.  A  gold  button-balance,  for  weighing  the  gold  beads 
from  the  assay  of  gold  ores.  This  balance  should  take  at 
least  0.5  gm.  in  each  pan,  and  should  be  sensitive  to  within 
TnT  mgm'  It  should  be  provided  with  a  set  of  weights  from 
I  mgm.  to  0.5  gm.,  and  a  beam-rider  for  weighing  fractions  of 
a  milligramme.  It  should  be  kept  in  a  glass  case,  free  from 
dust,  etc.,  and  should  be  provided  with  agate  knife-edges. 

The  last  three. balances  should  be  set  up  on  a  perfectly 
firm  support,  and  should  be  cleaned  and  adjusted  from  time  to 
time. 

The  balance  should  always  be  tested  before  weighing,  to 
see  if  it  is  in  perfect  adjustment. 

The  analytical  balance  should  be  provided  with  two  watch- 
glasses,  one  for  each  pan.  These  watch-glasses  are  made  with 
a  glass  lip  or  handle  for  convenience  in  removing.  If  they  are 
not  of  equal  weight,  one  can  be  filed  on  the  bottom  until  they 


APPARATUS  AND   OPERATIONS.  53 

counterbalance,  or  the  balance  can  be  brought  into  adjustment 
by  means  of  a  small  piece  of  platinum  foil  or  wire. 

Accurate  weighing  is  absolutely  essential  to  accurate  work. 
The  most  expeditious  way  of  ascertaining  the  exact  weight  of 
a  substance  is  to  avoid  trying  the  weights  at  random,  but  to 
proceed  in  a  methodical  manner.  Suppose,  for  example,  we 
wish  to  ascertain  the  weight  of  a  precipitate  whose  weight 
subsequently  turns  out  to  be  0.535  gm-  The  precipitate  is 
transferred  to  the  left-hand  pan  of  the  analytical  balance,  and 
a  i-gm.  weight  is  placed  in  the  right-hand  pan.  The  weight  is 
found  to  be  too  much;  so  it  is  replaced  by  a-o.5-gm.  weight, 
which  is  found  to  be  too  little.  A  o.i-gm.  weight  is  now 
added,  and  is  found  to  be  too  much  ;  so  it  is  replaced  by  a 
o.O5-gm.  weight,  which  is  found  to  be  still  too  much.  The 
o.O5-gm.  weight  is  replaced  by  the  0.02  and  the  two  o.oi-gm. 
weights,  which  is  found  to  be  still  too  much.  One  of  the  o.oi- 
gm.  weights  is  removed,  when  the  weight  is  found  to  be  too 
little ;  hence  the  O.oo5-gm.  weight  is  added.  The  balance  is 
found  to  exactly  balance;  hence  this  is  the  correct  weight.  It 
is  best,  in  order  to  have  a  check  on  the  weight,  to  add  up  the 
different  weights  on  the  pan  and  set  down  the  total.  As  the 
weights  are  removed  from  the  pan  each  weight  is  set  down, 
and  the  sum  taken  after  all  are  removed. 

The  balance  should  be  arrested  each  time  a  change  is  con- 
templated, such  as  removing  weights,  substituting  one  weight 
for  another,  etc. 

Substances  liable  to  attract  moisture  from  the  air  should 
always  be  weighed  in  closed  vessels — as  between  two  watch- 
glasses,  in  covered  crucibles,  or  in  a  closed  glass  tube.  The 
same  applies. to  substances  liable  to  lose  moisture  upon  expos- 
ure to  the  air. 

Fluids  should  be  weighed  in  small  bottles  provided  with 
glass  stoppers,  or  occasionally  in  accurately  counterpoised 
beakers. 

A  vessel  should  never  be  weighed  whilst  warm,  as  in  that 
case  its  weight  will  invariably  be  too  low.  This  is  due  to  two 
circumstances :  highly  heated  bodies  are  constantly  communi- 


54  A   MANUAL   OF  PRACTICAL   ASSAYING. 

eating  heat  to  the  surrounding  air;  the  heated  air  expands 
and  ascends,  and  the  denser  and  cooler  air  flowing  toward  the 
space  which  the  heated  air  leaves  produces  a  current,  which 
tends  to  raise  the  scale-pan.  Every  body  condenses  on  its 
surface  a  certain  amount  of  air  and  moisture,  which  amount 
depends  upon  the  temperature  and  the  hygroscopic  state  of 
the  air  and  the  temperature  of  the  body. 

In  weighing  out  a  substance  for  assay  or  analysis  it  is 
generally  best  to  take  a  certain  definite  quantity,  as  0.5  A.  T., 
O.I  A.  T.,  i.o  gm.,  0.5  gm.,  for  example,  rather  than  to  weigh 
out  an  indefinite  quantity,  as  0.946  gm.  Whilst  this  takes 
longer  in  the  weighing  out,  the  extra  time  expended  in  weigh- 
ing is  more  than  made  up  by  the  time  saved  in  the  subsequent 
calculations.  Moreover,  when  a  definite  even  quantity  is  taken, 
errors  in  the  subsequent  calculations  are  much  less  liable  to 
occur. 

Furnaces. — For  fusions  in  fire-assaying  either  the  wind-  or 
muffle-furnace  may  be  used.  As  the  muffle-furnace  is  cleaner, 
and  allows  of  a  more  perfect  control  of  the  heat,  it  is  preferable 
to  the  wind-furnace.  Where  samples  of  bullion,  etc.,  are 
to  be  melted,  it  will  be  necessary  to  have  a  wind-furnace; 
otherwise  not. 

Both  wind-  and  muffle-furnaces  are  built  to  use  either  solid 
or  gaseous  fuel.  The  gas-furnaces  have  several  advantages, 
inasmuch  as  they  allow  of  a  more  perfect  control  of  the 
temperature,  are  cleaner,  are  readily  started,  and  only  con- 
sume fuel  when  the  work  is  going  on.  On  account  of  the 
facility  with  which  the  temperature  can  be  controlled  the 
U.  S.  Government  ha\£  adopted  gas-furnaces  in  many  of  the 
Government  mints  and  assay-offices.  Gas-furnaces  can  only 
be  used  where  power  is  handy,  as  they  require  a  pressure- 
blower  to  furnish  the  necessary  blast.  They  are  no  more 
economical  in  fuel  than  furnaces  using  coal  or  coke,  but  are  to 
be  recommended  where  power  and  gas  are  at  hand,  for  the 
above  reasons.  Many  excellent  forms  are  kept  in  stock  by 
the  dealers. 

Where  solid  fuel  is  used  coke  or  charcoal  is  the  usual  fuel 


APPARATUS  AND   OPERATIONS. 


55 


in  the  wind-furnace,  and  coke  or  bituminous  fuel  in  the  muffle- 
furnace,  although  charcoal  is  also  used  in  the  muffle-furnace. 

The  ordinary  type  of  wind-furnace  built  for  coke  or  char- 
coal is  shown  in  Fig.  8.  This  furnace  is  built  of  red  bricl^and 
lined  with  one  course  of  fire-brick.  It  should  be  firmly  bound 
with  angle-iron,  and  tied  with  tie-rods.  The  top  of  the  furnace 


WIND  OR  CRUCIBLE  FURNACE 
Scale  Hin.-=1  ft. 

FIG.  8. 

is  covered  with  a  cast-iron  plate,  the  cover  or  lid  also  being  of 
cast  iron.  The  dimensions  of  the  furnace  shown  in  the  sketch 
can  be  increased  to  any  desired  extent,  but  the  same  relative 
dimensions  between  the  parts  should  be  maintained  when 
increasing  the  size.  Where  large  amounts  of  silver  bullion  are 
to  be  melted  the  furnace  will  necessarily  have  to  be  consider- 


A    MANUAL    OF  PRACTICAL   ASSAYING. 


ably  larger  than  shown  in  the  sketch.  Where  bullion  is  to 
be  melted  it  is  also  well  to  provide  the  furnace  with  a  chain- 
tackle  for  lifting  the  crucibles  out  of  the  furnace.  Where 
retort  silver  from  a  pan-amalgamation  mill  is  to  be  melted, 
the  furnace  should  be  provided  with  a  sheet-iron  hood,  con- 
nected with  the  stack,  for  carrying  off  the  fumes. 

There  are  many  different  styles  of  muffle-furnace  in  use. 
The  furnace   shown    in   Figs.  9  and    10  is  designed  to  burn 


MUFFLE  FURNACE  FOR  BITUMINOUS  COAL 
1    Seal  ejAin.-=  1ft.    • 


FIG.  g. 


FIG.  10. 


bituminous  coal.  Where  good  bituminous  coal  can  be  ob- 
tained, this  is  as  satisfactory  a  furnace  as  can  be  built.  The 
furnace  is  built  of  red  brick,  and  lined  throughout  with  one 
course  of  fire-brick.  It  should  be  firmly  bound  with  angle- 
iron,  tied  with  iron  tie-rods.  Where  good  bituminous  coal 
can  be  obtained,  this  furnace  is  preferable  to  a  coke-furnace 
for  the  following  reasons :  It  is  quickly  started,  the  tempera- 
ture is  readily  controlled,  the  consumption  of  muffles  is  much 
less  than  in  a  coke-furnace,  the  consumption  of  fuel  is  less  (in 


APPARA  TUS  AND    OPERA  T1ONS, 


57 


cost)  at  the  ordinary  pnces  of  coal  and  coke,  and  the  furnace 
has  a  longer  life. 

Figs.  II  and   12  show  a  furnace  constructed  to  burn  coke 


MUFFLE  FURNACE  FOR  COKE  OR  CHARCOAL, 
Scale  y4in.=1  ft. 

FIG.  ii.  FIG.  12. 

This  furnace  is  lined  throughout  with  fire-brick,  and  bound 
with  angle-iron  and  tie-rods. 

Heating  Apparatus. — The  fusion  of  substances  with  car- 
bonate of  soda  or  mixed  carbonates  can  be  performed  in  the 
muffle-furnace  or  over  a  blast-lamp.  Fletcher's  gas  blast-lamp 
will  be  found  almost  indispensable  in  a  laboratory  provided 
with  gas,  for  both  fusions  and  the  ignition  of  precipitates. 
Where  gas  is  not  at  hand,  Fletcher's  petroleum  blast-lamp  or 
an  alcohol  blast-lamp  may  be  used  for  fusions,  etc.  However, 
if  gas  is  not  at  hand,  the  muffle-furnace  best  answers  the  pur- 
pose, and  in  a  metallurgical  laboratory  where  a  great  number 
of  determinations  are  made  daily  the  muffle  is  preferable,  as 
it  allows  of  a  number  of  fusions  or  ignitions  to  be  made  at 
one  time. 

For  fusions  which  do  not  require  a  very  high  temperature, 
as  the  fusion  with  caustic  potash  or  the  fusion  with  potassium 
bisulphate,  the  Bunsen  burner  or  a  good  alcohol  lamp  is  all 
that  is  required. 


58  A  MANUAL  OF  PRACTICAL  ASSAYING. 

For  heating  solutions,  evaporations,  etc.,  the  gas-stove 
(Fletcher's)  is  an  excellent  piece  of  apparatus.  When  gas  is 
not  at  hand  a  petroleum-stove  can  be  substituted.  Where  a 
high  temperature  is  not  detrimental  the  top  of  the  stove  can 
be  covered  with  a  piece  of  wire-gauze.  Where  a  high  heat  is 
not  wanted  the  wire-gauze  can  be  covered  with  a  piece  of 
asbestos  paper  or  asbestos  cardboard. 

A  most  excellent  piece  of  apparatus  for  evaporations,  etc., 
•consists  of  a  sheet-iron  plate,  supported  on  four  legs.  This 
plate  can  be  heated  by  gas-  or  petroleum-stoves  or  Bunsen 
burners.  The  temperature  can  be  controlled  by  placing  under 
the  vessels  containing  the  solutions  pieces  of  asbestos  paper  of 
different  thicknesses. 

Large  vessels  which  are  liable  to  be  broken  by  the  ebullition 
during  heating  are  best  supported  on  a  sand-bath.  A  conven- 
ient form  of  sand-bath  is  an  ordinary  tin  pie-plate  partially 
filled  with  fine,  clean  sand. 

A  water-bath  will  be  essential  for  evaporations,  which 
should  not  be  heated  above  the  boiling  temperature  of  water. 
A  good  form  of  water-bath  is  a  water-tight  box  of  sheet  copper 
1 8  inches  long,  12  inches  wide,  and  4  inches  deep.  The  top 
should  have  several  round  holes  of  different  diameters,  so  that 
vessels  of  different  sizes  may  be  used  on  the  bath.  The  open- 
ings should  be  provided  with  covers,  so  that  they  may  be 
closed  when  not  in  use.  The  water-bath  is  partially  filled  with 
water,  and  the  heat  turned  on.  As  soon  as  the  water  reaches 
the  boiling-point  it  is  ready  for  use. 

Where  solutions  require  to  be  heated  at  a  definite  fixed 
temperature,  either  higher  or  lower  than  that  of  boiling  water, 
a  solution  of  calcium  chloride,  salt,  etc.,  can  be  substituted  for 
the  water  in  the  bath,  or  the  solution  may  be  evaporated  in  a 
hot-air  bath  which  is  kept  at  a  fixed  temperature. 

A  hot-air  bath  will  be  found  convenient  for  drying  precipi- 
tates, evaporation  of  solutions,  and  determinations  of  moisture 
in  certain  substances.  It  should  be  provided  with  a  thermom- 
eter, so  that  the  temperature  may  be  controlled. 

In   a  laboratory  where  gas   is  not   at   hand   a  very  good 


UNIVERSITY 
APPARATUS  AND    oPSEjfTffftfs.  59 

apparatus  for  evaporations,  etc.,  is  an  ordinary  cook-stove. 
The  evaporations  can  be  performed  on  the  top  of  the  stove, 
the  temperature  being  controlled  by  means  of  pieces  of  asbes- 
tos paper.  In  case  quite  high  temperatures  are  necessary, 
the  lids  of  the  stove  can  be  removed  and  asbestos  cardboard 
substituted  for  them.  The  oven  can  be  used  for  the  drying  of 
precipitates,  samples,  etc.  The  stove  should  be  provided  with 
a  hood  connected  with  a  good  draught  to  carry  off  the  fumes. 
This  hood  can  be  conveniently  made  of  wood  lined  on  the 
inside  with  asbestos  paper.  The  conduit  of  the  hood  may  be 
connected  with  the  same  flue  as  the  stove,  thus  insuring  a 
good  draught. 

Crucibles. — In  an  assay-office  doing  general  work  several 
different  kinds  of  crucibles  will  be  necessary. 

A.  Graphite  Criicibles. — These  are  used  for  the  melting  of 
samples  of  base  bullion,  silver  bullion,  gold  bullion,  etc.     The 
best  crucibles  are  made  by  the  Dixon  Crucible  Co.,  and  come 
in  different  sizes,  holding  from  4  ounces  up  to  5000  ounces. 
The  melting  is  performed  in  the  wind-furnace  as  follows :  A 
good  fire  is  started  in  the  furnace,  and  when  burning  well  the 
crucible  and  its  contents  are  introduced,  the  spaces  around  the 
outside  of  the  crucible  being  filled  in  with  fresh  coke  or  char- 
coal.    The  cover  is  then  put  on  the  furnace,  and  the  damper 
opened.     After  each  melt  the  crucible  should  be  thoroughly 
cleaned  whilst   hot   by  means  of   a  scraper.     With  proper  care 
a  crucible  will  serve  for  a  large  number  of  melts. 

B.  Clay  and  Sand  Crucibles. — These  are  used  for  the  fusion 
in  the  crucible  assay  of  gold  and  silver  ores,  and  also  for  the 
fusion-  or  fire-assay  of  ores  of  the  base  metals.     They  come  in 
a  great  variety  of  shapes  and  sizes,  those  most  used  being 
rated  as  5,  10,  20,  and  30  grammes  (capable  of  holding  charges 
for  the  assay  of  5,  10,  20,  and  30  grammes  of  ore).     The  best 
makes  are  the  Colorado  clay  (made  by  the  Denver  Fire-clay 
Co.),  the  French  clay,  the  Battersea  (English  make),  and  the 
Hessian  sand  (German  make).     In  the  western  portions  of  the 
United  States  the  Colorado-clay  crucible  has  generally  replaced 


60  A    MANUAL    OF  PRACTICAL   ASSAYING. 

the  other  makes,  owing  to  the  less  cost  of  these  crucibles  and 
their  general  excellence. 

C.  Porcelain  Crucibles. — These  are  used  for  the  ignition  of 
precipitates,    fusions   which   cannot   be   made   in   platinum   or 
silver  crucibles,  and  for  the  parting  and  annealing  of  the  gold: 
beads  obtained  in  the  assay  of  gold  and  silver  ores,  etc.     They 
come  in  a  great  variety  of  sizes,  the  best  makes  being  royal 
Berlin  china  and  royal  Meissen  porcelain. 

D.  Platinum  Crucibles. — These  are  used  for  the  fusion  of 
ores,  furnace  products,  etc.,  with  carbonate  of  soda,  etc.    They 
come  in  a  variety  of  sizes,  and  are  sold  by  the  gramme,  the 
present  price  being  about  65  cents  per  gramme.     They  weigh, 
with  the  cover,  about  as  many  grammes  as  they  hold  cubic 
centimetres.     As  they  are  expensive  they  should  be  handled 
carefully.     They  should  never  be  squeezed  in   the  ringers  to 
remove  the  fused  mass.     The  best  way  to  remove  a  fusion  is 
to  remove  the  crucible   from   the  heat  and  quickly  pour  its 
contents  out  on  a  piece  of  clean  platinum  (the  cover  of  a  large 
cruc.ible   answers  very  well),   or   just   before   the    fused   mass 
solidifies  insert  a  stout  piece  of  platinum  wire  in  it.     The  end 
of  the  wire  should  be  bent  in  the  form  of  a  hook.     As  soon  as 
the  mass  is  cool,  introduce  a  little  hot  water,  and  warm  gently; 
in  a  few  minutes  the  mass  may  be  lifted  out  by  means  of  the 
wire.     The  crucibles  may  be  cleaned  by  heating  with  a  little 
nitric  acid  (free  from  chlorine)  or  by  scouring  with  a  little  finely 
pulverized  red  iron  oxide. 

E.  Rose  Crucibles. — These  are  used  for  the  ignition  of  cer- 
tain precipitates,  which  require  to  be  ignited  in  an  atmosphere 
of  hydrogen,  sulphuretted  hydrogen,  etc.     They  are  made  of 
porcelain,  with  a  perforated  porcelain  cover  and   tube.     The 
tube  is  attached  to  the  supply  of  hydrogen  or  other  gas.     A 
very  good  substitute  for  a  Rose  crucible  is  an  ordinary  porce- 
lain crucible,  and  a  clay  tobacco-pipe  for  the  cover  and  tube.  ' 

F.  Silver    Crucibles. — These    are    used    for   fusions    where 
caustic  soda  or  caustic  potash  is  the  flux.     The  crucibles  with 
a  gold  lining  are  preferable.     An  alcohol-lamp  should  be  used 
to  heat  these  crucibles. 


APPARATUS  AND    OPERATIONS.  6 1 

Scorifiers. — These  are  used  in  the  scorification-assay  of 
gold  or  silver  ores.  They  come  in  the  following  sizes :  2j,  2j, 
3,  and  4  inches  diameter.  The  best  makes  are  the  Colorado 
(Denver  Fire-clay  Co.)  and  the  Battersea. 

Cupels. — The  cupels  used  for  the  cupellation  of  the  lead 
buttons  carrying  the  gold  and  silver  are  made  of  bone-ash,  the 
bones  of  horses  or  sheep  being  considered  the  best.  It  is  better 
to  make  the  cupels  than  to  buy  them  ready-made.  The  bone-ash 
is  mixed  with  sufficient  warm  water  to  hold  it  together  without 
being  too  moist.  By  adding  a  little  wood-ash  or  pearl-ash 
(potassium  carbonate)  to-  the  water  used  in  moistening  the 
bone-ash  the  cupels  will  be  more  firm.  The  cupels  are  pre- 
pared by  filling  the  mould  with  the  moistened  bone-ash,  and 
driving  the  pestle  with  two  or  three  light  blows  of  a  wooden 
mallet.  They  should  be  dried  carefully  by  standing  them  in  a 
warm  place  or  in  a  place  exposed  to  the  rays  of  the  sun,  and 
all  moisture  and  organic  matter  should  be  expelled  previous 
to  using  by  heating  them  in  the  muffle. 

Casseroles. — Casseroles  and  evaporating  dishes  are  used 
for  the  decomposition  of  ores,  etc.,  with  acids  and  other  liquid 
reagents,  and  for  the  evaporation  of  solutions.  They  are  of 
porcelain  and  platinum,  the  porcelain  being  most  generally 
used.  .They  come  in  a  variety  of  sizes  holding  from  %  ounce 
up  to  -J-  gallon.  A  very  convenient  size  is  the  ^-ounce  casse- 
role, which  is  2  inches  in  diameter.  The  best  makes  are  royal 
Berlin  china,  royal  Berlin  porcelain,  and  German  porcelain. 

Beakers. — Beakers  serve  for  a  variety  of  uses  in  the  labo- 
ratory. Lipped  beakers  are  always  preferable.  Bohemian- 
glass  beakers  are  the  best.  They  come  in  a  number  of  sizes, 
ranging  from  -J  ounce  up  to  200  ounces  in  capacity. 

Beaker  covers  of  convex  glass  (watch-glasses)  will  be  found 
indispensable. 

Funnels  and  Filtering. — The  best  funnels  are  made  of  the 
best  Bohemian  or  the  best  German  glass.  They  come  in  a 
variety  of  sizes,  ranging  in  capacity  from  I  ounce  to  I  gallon. 
They  are  also  made  in  a  variety  of  different  forms  for  special 
purposes. 


62  A    MANUAL    OF  PRACTICAL  ASSAYING. 

There  are  a  number  of  different  makes  of  filter-paper,  of 
which  Schleicher  &  Schuell's  and  Munktell's  best  Swedish  are 
the  best  for  quantitative  work. 

The  best  form  of  glass  rods  for  filtering  are  made  by  cutting 
glass  tubing  into  suitable  lengths,  and  sealing  the  ends  by- 
means  of  the  blast-lamp.  They  are  light,  and  there  is  less 
liability  of  fracturing  the  beakers  than  in  the  case  of  solid- 
glass  rods. 

In  preparing  a  funnel  for  filtration  the  paper  should  always 
fit  tight  to  the  sides,  and  should  be  moistened  with  water  after 
placing  it  in  the  funnel.  In  pouring  a  stream  from  the  beaker 
on  to  the  filter  the  stream  should  always  be  poured  against  a. 
glass  rod.  The  under  side  of  the  lip  of  the  beaker  should 
always  be  dry.  In  filtering,  the  rods  should  not  have  rubbers 
on  the  end,  as  they  are  liable  to  introduce  organic  matter  into 
the  solutions.  Rubbers  on  the  rods  are  used  in  cleaning  the 
beakers,  and  sometimes  in  removing  the  last  particles  of  a 
precipitate  from  the  beaker  or  casserole. 

Always  use  as  small  a  filter  as  will  allow  of  the  proper 
washing  of  its  contents.  In  washing  allow  all  the  solution  to 
run  through  the  filter  before  adding  any  wash-water.  Fill  up 
the  filter  with  the  water,  and  allow  that  to  run  through  before 
adding  any  more.  By  this  means  excessive  quantities  of  wash- 
water  may  be  avoided.  In  washing  by  decantation,  which  is 
sometimes  necessary,  allow  the  precipitate  to  settle,  decant  as 
closely  as  possible,  pouring  the  solution  on  the  filter ;  add 
water,  stir  well,  allow  to  settle,  and  decant  again  closely  before 
adding  more  wash-water. 

A  filter-pump  will  be  found  a  great  convenience  in  a 
laboratory  where  many  bulky  precipitates  are  to  be  washed. 
Richards'  filter-pump,  for  water-pressure,  is  the  best  where 
water-pressure  can  be  obtained.  Where  water-pressure  cannot 
be  obtained  Bunsen's  filter-pump  is  the  best. 

After  a  precipitate  is  thoroughly  washed  the  funnel  should 
be  removed  with  the  filter  from  the  filter  rack,  and  the  precipi- 
tate thoroughly  dried  with  the  filter  before  ignition.  When  a 


APPARATUS  AND   OPERATIONS.  65 

filter-pump  is  used  the  precipitate  and  filter  can  be  partially 
dried  rapidly  by  drawing  air  through  by  means  of  the  pump. 

Flasks. — The  best  flasks  are  made  of  the  best  Bohemian 
glass.  A  number  of  flasks  of  different  sizes  and  different  kinds 
will  be  found  useful.  Flat-bottom  flasks  of  8,  16,  and  24  ounce 
capacity,  provided  with  double  perforated  rubber  stoppers,  are 
useful  for  making  wash-bottles.  Pear-shaped  flasks  of  4  and  6 
ounce  capacity  will  be  found  useful  for  copper  determinations 
and  for  decomposing  ores,  etc.  Filtering  flasks  of  I  and  2 
pints  capacity,  and  of  heavy  glass,  are  useful,  especially  where 
the  filter-pump  is  used.  A  set  of  volumetric  flasks,  accurately 
graduated,  and  provided  with  ground-glass  stoppers,  will  be 
indispensable  for  volumetric  analysis.  The  following  makes 
a  convenient  set :  50  cc.,  100  cc.,  250  cc.,  500  cc.,  and  1000  cc. 
They  should  not  only  be  accurately  graduated,  with  two  marks 
on  the  neck  of  each,  one  called  the  holding-mark  (the  capacity 
Df  the  flask  when  filled  to  that  mark),  and  the  other  called  the 
delivery-mark  (the  number  of  cubic  centimetres  the  flask  will 
deliver  when  filled  to  that  mark),  but,  which  is  most  important, 
they  should  be  graduated  so  that  they  will  bear  the  same  rela- 
tive ratio  to  each  other  ;  that  is,  the  loo-cc.  flask  should  hold  just 
half  as  much  as  the  2OO-cc.  flask,  and  the  looo-cc.  flask  should 
hold  just  four  times  as  much  as  the  25o-cc.  flask  when  each  is 
filled  to  the  holding-mark.  This  is  of  the  utmost  importance 
in  volumetric  analysis  where  aliquot  portions  are  frequently 
taken. 

If  it  is  desired  to  standardize  a  flask  with  great  accuracy  it 
can  be  done  by  counterpoising  the  flask  on  the  balance  with 
any  convenient  weight,  adding  weights  to  those  on  the  balance 
to  an  amount  corresponding  to  the  desired  capacity  of  the 
flask,  adding  the  proper  amount  of  .water,  and  marking  the 
neck  of  the  flask  with  the  aid  of  a  diamond  or  a  good  steel 
file.  If  an  accurately  standardized  flask  or  pipette  is  at  hand, 
others  of  twice,  thrice,  etc.,  its  capacity  can  readily  be  pre- 
pared. 

Pipettes  and  Burettes. — These  are  constantly  used  in 
volumetric  /malysis.  They  are  best  purchased  already  gradu- 


64  A    MANUAL    OF  PRACTICAL   ASSAYING. 

ated,  but  their  capacity  should  always  be  tested,  especially  as 
against  the  other  measuring  apparatus  on  hand,  and  as  against 
each  other. 

To  test  the  capacity  of  a  pipette,  fill  it  to  the  proper  mark 
with  distilled  water  of  16°  C.,  run  this  water  into  a  weighed 
flask  or  beaker,  and  weigh  the  amount  delivered.  This  weight 
should  nearly  correspond  in  grammes  to  the  capacity  of  the 
pipette  in  cubic  centimetres.  A  slight  difference  should  be 
allowed  for  the  expansion  of  water  between  o°  and  16°  C. 
One  cc.  of  distilled  water  at  16°  C.  weighs  0.9988  gramme. 
In  like  manner  the  accuracy  of  a  burette  may  be  verified  by 
weighing  the  amount  delivered,  taking  any  even  number  of 
cubic  centimetres. 

A  pipette  should  always  be  filled  by  suction  to  a  little 
above  the  mark ;  then,  by  closing  the  top  with  the  finger,  the 
liquid  may  be  allowed  to  run  slowly  out  until  the  lower  part 
of  the  meniscus  is  at  the  line.  It  will  then  (if  correct)  deliver 
the  number  of  cubic  centimetres  marked  upon  it.  Pipettes 
may  have  both  a  holding-  and  delivery-mark,  but  if  used  for 
delivery  only  the  holding-mark  is  unnecessary. 

There  are  many  different  forms  of  burettes  made,  but  those 
of  Mohr  and  Gay-Lussac  are  the  most  convenient,  and  gener- 
ally preferred.  Mohr's  burette,  provided  with  Geissler's  glass 
stop-cock  or  the  Gay-Lussac  burette,  should  always  be  used 
for  solutions  liable  to  decompose  rubber. 

In  a  laboratory  where  the  volumetric  solutions  are  in 
constant  use  it  is  a  good  plan  to  have  a  separate  burette  for 
each  standard  solution,  and  attach  it,  by  means  of  a  siphon, 
of  glass  tubing,  and  a  glass  stop-cock,  to  the  bottle  holding  the 
standard  solution.  By  this  means  the  burettes  are  readily 
filled,  and  do  not  have  to  be  emptied  and  cleaned  after  each 
set  of  determinations. 

As  the  success  of  volumetric  analysis  depends  largely  upon 
accurate  measuring,  too  much  care  cannot  be  given  to  accu- 
rately graduating  and  reading  the  flasks,  pipettes,  and  burettes. 

Tools. — A  number  of  small  tools  will  be  required  as 
follows :  A  set  of  three  hammers,  for  pounding  lead  buttons, 


APPARATUS  AND    OPERATIONS.  65 

flattening   silver-gold    buttons   for    parting,    and    cutting   out 
samples  of  bullion,  etc. ; 

Shovels  and  pokers,  and  scrapers  for  cleaning  out  the  muffle  ; 

Crucible  tongs,  scorifier  tongs,  and  cupel  tongs,  for  fire- 
work. Small  crucible  tongs,  for  crucibles  used  in  wet  assays ; 

Cold-chisels,  for  cutting  out  samples  of  bullion  ; 

A  small  anvil  or  steel  plate,  for  hammering  lead  buttons 
and  separating  the  buttons  from  the  slag ; 

Spatulas,  for  sampling,  weighing  out,  mixing  charges,  etc.  ; 

A  set  of  small  steel  dies,  from  o  to  9  inclusive,  for  marking 
bars  and  samples  of  bullion  ; 

A  pair  of  cutting  shears  and  nippers,  for  cutting  samples  of 
bullion,  etc.  ; 

A  pair  of  scissors,  for  cutting  filter-papers,  and  a  set  of  filter 
patterns ; 

Files,  for  cutting  glass  rods  and  tubing,  marking  flasks,  etc. ; 

An  assorted  lot  of  rubber  stoppers,  both  perforated  and 
plain  ; 

An  assorted  lot  of  glass  tubing  and  glass  rods ; 

An  assorted  lot  of  rubber  tubing  ; 

Platinum-wire  and  platinum-foil. 

Whilst  most  of  the  apparatus  used  in  the  analytical  work 
can  be  purchased  of  the  dealers,  a  great  deal  of  it  can  be  made 
in  the  laboratory  with  a  little  patience  and  ingenuity.  The 
student  should  accustom  himself  to  make  such  odd  pieces 
of  apparatus  as  he  requires,  as  the  chemist  frequently  needs 
apparatus,  and  cannot  wait  until  it  can  be  obtained  from  some 
distant  dealer. 

In  purchasing  apparatus  and  supplies  always  buy  the  best, 
as  cheap  apparatus  is  dear  at  any  price.  Do  not  be  extrava- 
gant in  your  purchases,  as  it  is  not  necessary  to  have  an 
immense  amount  of  costly  apparatus  on  hand  in  order  to  do 
good  work. 


CHAPTER  V. 

REAGENTS. 

THE  reagents  used  in  both  wet  and  dry  assaying  may  be 
divided  into  the  following  general  classes  : 

Fluxes. — This  class  includes  a  large  number  of  bodies,  but 
generally  they  are  substances  which  render  others  to  which  they 
are  added  more  fusible,  either  by  acting  as  solvents  or  as  de- 
composing agents.  They  are  either  acid,  basic,  or  neutral  in 
.their  action. 

The  following  are  the  principal  fluxes  used  in  wet  assaying 
or  chemical  analysis  : 

Carbonate  of  Soda  (Na2CO3).  This  acts  as  a  decomposing 
agent,  and  is  used  for  the  decomposition  by  fusion,  either 
alone  or  in  conjunction  with  other  reagents,  of  silicates,  etc. 
It  should  be  pure,  and  free  from  moisture. 

Carbonate  of  Potassium  (K2CO8).  This  acts  the  same  as 
sodium  carbonate,  with  which  it  is  frequently  mixed.  A 
mixture  of  the  two  carbonates  in  the  proportion  of  their 
molecular  weights  is  a  most  excellent  flux  for  the  decomposi- 
tion of  certain  silicates,  clays,  etc.,  which  are  difficultly  decom- 
posed by  either  carbonate  when  used  alone.  The  potassium 
carbonate  should  be  pure  and  free  from  moisture. 

Potassium  Bisulphate  (KHSO4).  This  acts  both  as  a  de- 
composing agent  and  as  an  acid  flux.  Silica  is  not  rendered 
soluble  by  fusion  with  this  reagent,  whilst  iron  oxide,  alumina, 
etc.,  are  converted  into  a  form  which  is  soluble. 

66 


REAGENTS.  6? 

Sodium  Hydrate  (NaOH).  This  acts  both  as  a  decom- 
posing agent  and  a  basic  flux.  It  is  used  principally  for  the 
decomposition  of  sulphides  and  sulphates  in  the  determination 
of  sulphur.  It  is  occasionally  used  for  the  decomposition  of 
certain  silicates  and  oxides,  and  is  particularly  adapted  to  the 
decomposition  of  certain  organic  compounds,  converting  them 
into  compounds  which  are  soluble  in  water. 

Potassium  Hydrate  (KOH).  This  acts  the  same  as  sodium 
hydrate,  and  is  used  for  the  same  purposes. 

Sodium  Nitrate  (NaNO3).  This  acts  as  a  decomposing 
agent,  and  also  as  an  oxidizer.  It  should  be  pure,  and  free 
from  moisture.  The  corresponding  potash  salt  (KNO3)  is  also 
used  for  the  same  purposes. 

Hydrofluoric  Acid  (HF1).  This  is  one  of  the  most  power- 
ful decomposing  agents,  and  by  its  means  many  silicates  are 
decomposed,  the  silica  being  volatilized. 

The  following  are  the  principal  fluxes  used  in  dry  or  fire- 
assaying  : 

Sodium  Bicarbonate  (NaHCO3),  or  the  corresponding  potas- 
sium salt.  These  act  as  desulphurizing  agents,  as  basic  fluxes, 
and  in  some  cases  as  oxidizing  agents.  They  should  be  free 
from  moisture  and  coarse  particles.  As  they  are  readily 
fusible,  they  can  retain  in  suspension  a  large  proportion  of 
pulverized  infusible  substances  without  losing  their  fluidity. 

Borax,  crystallized  (2NaBO2,  B2O3,  ioH2O).  This  acts  as 
an  acid  flux,  and  is  sometimes  used  as  a  cover  in  place  of  salt. 
As  it  contains  a  large  amount  of  water,  it  is  usually  used  in  a 
vitrified  condition.  It  loses  its  water  readily  upon  fusion.  To 
prepare  the  vitrified  borax  (borax-glass),  fuse  it  in  an  iron-  or 
chalk-lined  clay  crucible,  pour  the  fused  mass  out  on  a  clean 
surface,  and  pulverize  when  cold. 

Litharge  (PbO).  Acts  as  a  basic  flux,  an  oxidizing  and 
desulphurizing  agent,  and  supplies  the  necessary  lead  in  the 
gold  and  silver  crucible  assay.  It  should  be  free  from  red 
oxide  of  lead.  White  lead  is  sometimes  used  in  its  place.  As 
it  always  contains  silver,  its  silver  contents  should  be  deter- 
mined and  deducted  from  the  results  of  all  silver  assays. 


68  A   MANUAL    OF  PRACTICAL  ASSAYING. 

Silica  (SiOa).  This  acts  as  an  acid  flux.  Sometimes  pow- 
dered  glass  is  substituted  for  silica.  Lime-glass  makes  the 
best  flux,  and  when  used  for  lead  assays  should  be  free  from 
lead. 

Lead  Flux.  This  is  a  mixture  of  sodium  bicarbonate  (16 
parts),  potassium  carbonate  (16  parts),  flour  (8  parts),  and 
borax-glass  (4  parts).  This  acts  as  a  flux,  reducing  agent,  and 
desulphurizing  agent.  It  is  especially  useful  in  the  lead  assay, 
and  frequently  forms  the  basis  of  the  charge  in  the  crucible 
assay  of  gold  and  silver  ores. 

Black  Flux.  This  consists  of  one  part  nitre  and  three  parts 
argol  (deflagrated).  It  is  not  much  used. 

Black  Flux  Substitute.  This  consists  of  a  mixture  of  flour 
(3  parts)  and  sodium  bicarbonate  (10  parts).  It  is  sometimes 
used  in  place  of  lead  flux. 

Potassium  Cyanide  (KCN).  Acts  as  a  powerful  reducing 
and  desulphurizing  flux.  It  is  frequently  used  for  the  determi- 
nation of  lead,  tin,  bismuth,  and  antimony  by  fire-assay.  For 
this  purpose  it  should  be  quite  pure,  and  free  from  sulphides 
and  sulphates. 

Argol  (KHC4H4O6).  Commercial  bitartrate  of  potash. 
This  acts  as  a  powerful  reducing  agent,  and  also  as  a.  basic 
flux.  Its  reducing  power  should  be  determined  by  fusion  with 
litharge  and  sodium  bicarbonate. 

Charcoal  (C).  Acts  as  a  reducing  agent  and  desulphurizes 
Its  reducing  power  should  be  determined. 

Salt  (Nad).  Is  used  principally  as  a  cover  in  crucible 
assays. 

Nitre  (KNO,).  This  acts  as  a  basic  flux  and  powerful  oxid- 
izing agent.  Its  oxidizing  power  should  be  determined.  To 
determine  its  oxidizing  power,  make  up  the  following  charge, 
place  it  in  a  clay  crucible,  and  fuse  in  a  hot  fire.  Remove, 
pour  cool,  and  weigh  the  lead  button.  The  difference  be- 
tween the  weight  of  the  button  obtained  and  that  given  in  the 
determination  of  the  reducing  power  of  the  charcoal,  divided 
by  1.5,  gives  the  oxidizing  power  of  the  nitre  per  gramme. 


REAGENTS.  69 

Charge. — Litharge 30  gms. 

Soda  bicarb 15     " 

Charcoal 0.5  " 

Nitre 1.5  " 

Metallic  Iron  (Fe).  Acts  as  a  basic  flux  and  desulphurizing 
agent.  Nails  or  iron  wire  about  -J  inch  in  diameter  are  the 
most  convenient  form. 

Metallic  Lead  (Pb).  This  acts  as  a  basic  flux  and  as  a  solv- 
ent or  collector  of  the  precious  metals  in  the  assay  of  gold  and 
silver  ores.  It  is  used  in  the  form  of  granulated  lead  in  the 
scorification  assay  and  in  the  form  of  sheet  lead  in  the  bullion 
assay.  As  it  is  never  free  from  silver,  its  silver  contents  should 
be  determined  and  the  proper  deduction  made  from  the  results 
of  all  silver  assays. 

All  of  the  above  fluxes  should  be  dry  and  pulverized. 

Solvents. — Whilst  many  of  the  fluxes  described  above  act 
as  solvents  during  fusion,  only  such  solutions  as  act  as  sol- 
vents in  wet  analysis  will  be  discussed. 

Water  (H2O).  Water  used  in  quantitative  analysis  for  so- 
lution, dilution,  etc.,  should  always  be  distilled. 

Hydrochloric  Acid  (HC1).  This  acts  as  a  powerful  solvent 
either  alone  or  in  conjunction  with  other  acids.  Aqua  regia 
(2HC1  +  HNO3)  is  one  of  the  most  powerful  solvents,  and  the 
only  acid  in  which  gold  and  platinum  are  soluble  to  any  great 
extent.  It  should  be  pure,  and  kept  on  hand  of  two  strengths, 
concentrated  and  dilute.  The  specific  gravity  of  dilute  hydro- 
chloric acid  should  be  1.2. 

Nitric  Acid  (HNO3).  Is  a  powerful  solvent  and  oxidizing 
agent.  It  should  be  pure,  and  kept  on  hand  in  concentrated 
and  dilute  state.  Fuming  nitric  acid  is  a  most  powerful  oxid- 
izing and  desulphurizing  agent.  The  specific  gravity  of  the 
dilute  nitric  acid  should  be  1.2. 

Sulphuric  Acid  (H2SO4).  Is  a  powerful  solvent,  and  is 
extensively  used  both  as  a  solvent  and  a  precipitant.  The 
specific  gravity  of  the  concentrated  acid  is  1.84.  The  dilute 


7O  A    MANUAL    OF  PRACTICAL  ASSAYING. 

acid  is  prepared  by  adding  one  volume  of  the  concentrated 
acid  to  five  volumes  of  water. 

Acetic  (HC2H302),  Oxalic  (H2C2O4),  Citric  (H.C.H.O, ,  HfO), 
and  Tartaric  Acids  (H3C4H4O6)  are  weak  solvents,  and  are  much 
used  for  special  purposes.  Acetic  acid  comes  in  solution 
either  as  commercial,  c.  p.  ordinary,  c.  p.  glacial  (99  p.  c.),  or 
c.  p.  anhydrous.  The  other  acids  come  in  the  crystalline 
form,  either  commercial  or  c.  p.  In  making  up  solutions  of 
these  acids  it  is  best  to  use  an  excess  of  the  reagent  and  make 
a  saturated  solution. 

Ammonium  Acetate  (NH4C2H3O2).  Is  a  powerful  solvent  of 
lead  salts,  especially  lead  sulphate.  The  reagent  is  best  made 
by  adding  strong  acetic  acid  to  strong  ammonia-water  until 
the  solution  is  just  acid,  and  then  add  a  few  drops  of  ammonia 
to  render  the  solution  alkaline.  The  corresponding  salts  of 
ammonia  with  citric  or  tartaric  acids  answer  the  same  purpose, 
but  are  more  expensive  and  no  better  than  the  acetate. 

Ammonia  (NH4OH).  Acts  as  a  powerful  solvent  of  chlo- 
ride and  bromide  of  silver. 

Sodium  Hyposulphite  (Na2H2S2O4).  Is  a  solvent  of  silver 
chloride,  and  is  used  largely  in  the  lixiviation  of  silver  ores. 

Potassium  Cyanide  (KCN).  Is  a  solvent  of  gold  and  silver, 
and  is  extensively  used  in  the  leaching  of  gold  ores. 

Ammonium  Sulphide  [(NH4)2SJ.  Is  a  powerful  solvent  of 
the  sulphides  of  arsenic,  antimony,  and  tin. 

Precipitants. — There  are  a  great  number  of  precipitants 
used  in  wet  analysis.  Only  a  few  of  the  more  important  will 
be  discussed. 

Barium  Chloride  (BaCl2).  Is  used  principally  c.3  a  precipi- 
tant for  sulphuric  acid.  In  making  up  the  solution  one  gm.  of 
the  crystalline  salt  is  added  to  10  cc.  of  water.  One  cc.  of  this 
solution  will  precipitate  0.0327  gm.  SO3. 

Hydrodisodic  Phosphate  (Na2HPO4).  Is  used  principally  as 
a  precipitant  for  magnesia.  In  making  up  the  solution  I  gm. 
of  the  crystalline  salt  is  added  to  10  cc.  of  water.  One  cc.  of 
this  solution  will  precipitate  0.0112  gm.  of  MgO. 


REAGENTS.  J I 

Ammonium  Oxalate  [(NH4)C2OJ.  Is  used  principally  as  a 
precipitant  for  calcium.  In  making  up  the  solution  I  gm.  of 
the  salt  is  added  to  10  cc.  of  water.  One  cc.  of  this  solution 
will  precipitate  0.0145  gm.  CaO. 

Magnesia  Mixture.  Is  used  as  a  precipitant  for  phosphorus 
and  arsenic.  In  making  up  the  solution  i  gm.  of  MgSO4  (salt), 
I  gm.  of  NH4C1  (salt),  and  4  cc.  of  ammonia  are  added  to  8  cc. 
of  water.  One  cc.  of  this  solution  will  precipitate  0.02^  gm. 

of  P.O.- 

Molybdate  Solution.  Is  used  as  a  precipitant  for  phosphorus 
and  arsenic.  In  making  up  the  solution  i  gm.  MoO3  is  dis- 
solved in  4  cc.  of  ammonia  and  the  solution  is  poured  into  15 
cc.  of  HNO3  (sp.  gr.  1.2).  One  cc.  of  this  solution  will  precip- 
itate 0.0013  gm.  of  P2Q6. 

Silver  Nitrate  (AgNO3).  Is  used  principally  as  a  precipitant 
for  chlorine.  In  making  up  the  solution  I  gm.  of  salt  is  added 
to  20  cc.  of  water.  One  cc.  of  this  solution  will  precipitate 
0.0104  gm.  of  Cl. 

Potassium  Permanganate  (K2Mn2O8).  Is  used  as  a  precipi- 
tant of  MnO2  in  the  volumetric  estimation  of  manganese.  The 
solution  is  made  up  in  the  manner  described  in  Part  II,  Chap- 
ter XVI. 

Ammonia  (NH4OH).  Is  used  as  a  precipitant  of  iron,  alu- 
mina, etc.,  and  is  an  indispensable  reagent  in  the  laboratory. 

The  strongest  concentrated  ammonia  has  a  sp.  gr.  of  0.88. 
This  diluted  with  two  volumes  of  water  has  a  sp.  gr.  of  0.96, 
which  is  the  reagent  commonly  used. 

Ammonium  Carbonate  [(NH4)2CO3].  Is  used  as  a  precipi- 
tant of  Zn,  Mn,  Fe,  Ca,  Ba,  etc.  Is  an  invaluable  reagent.  In 
making  up  the  solution  i  gm.  of  the  salt  and  i  cc.  of  ammonia 
are  added  to  4  cc.  of  water. 

'Ammonium  Sulphide  [(NH4)2S].  Is  used  as  a  precipitant 
of  Fe,  Zn,  Mn,  Ni,  and  Co.  To  prepare  the  solution  pass  a  rapid 
current  of  pure  sulphuretted  hydrogen  through  a  solution  of 
ammonia  in  the  reagent  bottle.  Should  be  kept  corked,  and  in 
a  dark,  cool  place.  As  it  loses  its  strength  rapidly,  it  is  best 
to  prepare  freshly  from  time  to  time. 


?2  A   MANUAL    OF  PRACTICAL  ASSAYING. 

Ammonium  Chloride (NH4C1).  Is  used  in  conjunction  with 
ammonia  as  a  precipitant  of  iron,  etc.  It  is  best  to  prepare  a 
saturated  solution. 

Sodium  Carbonate  (Na2Co3).  Is  used  as  a  precipitant  of  Zn, 
Fe,  Mn,  Ca,  Ba,  etc.  A  saturated  solution  is  usually  used. 

Sodium  Sulphide  (NaaS).  Is  used  principally  as  a  precipi- 
tant of  the  heavier  metals  and  as  a  solvent  for  sulphides  of  ar- 
senic, antimony,  and  tin.  To  prepare  the  solution  add  I  gm. 
of  salt  to  10  cc.  of  water. 

Sodium  and  Potassium  Hydrates  (NaOH  and  KOH).  Are 
used  as  precipitants  of  Cu,  Fe,Al4O3 ,  etc.  To  prepare  the 
solution  dissolve  I  gm.  of  the  salt  in  10  cc.  of  water. 

Sodium  Acetate  (NaC2H3O2).  Is  used  as  a  precipitant  of 
iron  and  alumina  in  the  basic-acetate  separation  of  these 
metals.  The  salt  is  generally  used. 

Sodium  Chloride  (NaCl)  and  Sodium  Bromide  (NaBr).  Are 
used  as  precipitants  of  silver  in  the  volumetric  estimation  of 
silver  (Part  III,  Chap.  II)  and  in  the  special  method  for  copper 
mattes  (Part  III,  Chap.  IV). 

Platinic  Chloride  (PtCl4).  Is  used  as  a  precipitant  of  potas- 
sium. To  prepare  the  solution  dissolve  I  gm.  of  the  metal  in 
aqua  regia,  evaporate  to  dryness  and  dissolve  in  I  cc.  HC1  and 
9  cc.  of  water.  One  gramme  of  this  solution  will  precipitate 
0.048  gm.  of  K2O. 

Hydric  Sulphide  (Sulphuretted  hydrogen,  H2S).  Is  used 
principally  as  a  precipitant  of  the  heavy  metals.  To  prepare 
the  gas  add  dilute  sulphuric  acid  to  pure  iron  sulphide.  The 
gas  should  be  washed  by  passing  it  through  water  before  using. 
If  pure  iron  sulphide  is  not  at  hand  it  can  be  prepared  by  fus- 
ing iron  nails  with  sulphur  in  the  proportion  of  about  I  part 
•iron  to  2,  parts  sulphur,  by  weight.  A  very  convenient  gen- 
erator is  shown  in  Figure  13. 

Sulphuric  Acid  (H2SO4).  As  a  precipitant,  is  used  princi- 
pally to  precipitate  barium.  One  cc.  of  the  dilute  acid  will 
precipitate  0.4291  gm.  Ba. 

Metallic  Zinc  (Zn).     It  is  used  for  the  precipitation  of  Pb, 


REAGENTS.  73 

Cu,  As,  Sb,  Ag,  and  Au  (from  cyanide  solutions).  The  zinc 
should  be  free  from  these  metals,  and  free  from  iron  when  used 
for  the  reduction  of  iron  solutions.  It  is  used  in  the  form  of 
sticks,  sheets,  or  as  granulated,  zinc.  To  granulate,  melt  some 
bar  zinc  in  a  clay  crucible,  skim  off  the  surface,  and  pour  into 
cold  water  from  a  considerable  height. 

Metallic  Copper  (Cu).  Is  used  as  a  precipitant  of  mercury. 
Comes  in  the  form  of  thin  foil  and  sheets. 

Metallic  Aluminium  (Al).  Is  used  as  a  precipitant  of  Cu 
and  Bi.  Comes  as  foil. 

Metallic  Lead  (Pb).  Is  used  as  a  precipitant  for  cop- 
per. Either  sheet  lead,  or  preferably  granulated  test-lead,  is 
used. 

Pure  materials  should  always  be  used.  In  making  up  the 
solutions  distilled  water  should  be  used.  The  salts  obtained 
from  the  dealers  and  labelled  "  chemically  pure  "  are  seldom 
absolutely  so,  and  often  afford  a  sediment  or  precipitate  when 
the  solutions  are  allowed  to  stand.  Hence  it  is  best  to  prepare 
the  solutions  in  bulk  and  filter  them  off  after  they  have  been 
allowed  to  stand  for  some  time.  Tests  should  always  be  made 
for  such  impurities  as  are  liable  to  interfere,  or  cause  error  in 
the  analyses.  If  such  impurities  are  found,  the  amount  will 
have  to  be  determined  and  an  allowance  made  for  it  in  the 
work,  either  by  carefully  measuring  the  amount  of  reagent  used 
and  making  the  proper  deduction  from  the  result  of  the  analy- 
sis, or  by  running  a  blank  analysis.  The  latter  course  is  gen- 
erally preferable  where  really  accurate  results  are  required.  In 
running  a  blank  analysis  the  same  amounts  and  kinds  of  re- 
agents are  added  to  the  proper  amount  of  water  as  are  used  in 
the  regular  analysis.  The  solution  is  boiled,  filtered,  etc.,  as  in 
the  regular  analysis.  The  weight  of  the  final  precipitate  ob- 
tained in  the  blank  analysis  should  be  deducted  from  the 
weight  of  the  precipitate  obtained  in  the  regular  analysis. 

Reducing  Reagents.— To  this  class  belong  those  bodies 
which  have  the  power  of  removing  oxygen  from  its  com- 
pounds. They  are  the  reverse  of  oxidizing  reagents. 


74  A   MANUAL    OF  PRACTICAL   ASSAYING. 

The  principal  reducing  reagents  used  in  fire-assaying  are 
as  follows:  Charcoal,  Argol,  Flour,  Starch,  Sugar,  Potassium 
Ferrocyanide,  and  Potassium  Cyanide.  They  have  been  dis- 
cussed under  the  head  of  "  Fluxes." 

The  following  are  the  principal  reducing  reagents  used  in 
wet  analysis : 

Hydrogen  (H).  This  is  the  most  powerful  reducing  agent. 
Is  used  in  the  form  of  a  gas,  which  should  be  dry  and  free  from 
impurities,  such  as  arseniuretted  hydrogen.  It  is  best  prepared 
by  treating  zinc,  or  iron  filings,  with  dilute  sulphuric  acid. 
Sometimes  dilute  hydrochloric  is  substituted  for  the  sulphuric 
acid.  The  gas  is  frequently  generated  in  the  solution  to  be 
reduced  as  in  the  case  of  the  reduction  of  a  solution  of  ferric 
sulphate  to  ferrous  sulphate  in  the  determination  of  iron.  (See 
Part  II,  Chap.  XVI.) 

Sulphuretted  Hydrogen  (HaS).  Is  a  powerful  reducing  agent. 
The  gas  is  generated  in  the  manner  described  under  the  head 
of  "  Precipitartts." 

Sodium  Sulphite  (Na2SO3).  This  is  a  good  reducing  agent. 
It  is  frequently  used  for  the  reduction  of  ferric  solutions.  It 
separates  Arsenious  Sulphide,  which  is  soluble  in  it,  from  the 
sulphides  of  antimony  and  tin,  which  are  insoluble  in  it. 

Stannous  Chloride  (SnCla).  This  is  frequently  used  for  the 
reduction  of  iron  solutions  for  the  volumetric  estimation  of 
iron.  (See  Part  II,  Chap.  XVI.) 

There  are  many  organic  compounds,  as  solutions  of  sugar, 
tartaric  acid,  etc.,  which  serve  as  reducing  agents. 

Oxidizing  Reagents.— Under  this  heading  are  comprised 
all  bodies  which  readily  yield  up  their  oxygen. 

The  principal  oxidizing  reagents  used  in  fire-assaying  are 
Nitre,  Litharge,  Sodium  Bicarbonate,  and  Ferric  Oxide. 

The  principal  oxidizing  reagents  used  in  wet  analysis  are 
the  following: 

Oxygen  (O).  This  is  the  most  powerful  oxidizing  agent, 
and  is  generated  or  produced  in  various  different  ways. 

Chlorine  (Cl).  Is  a  powerful  oxidizer,  and  is  readily  gener- 
ated by  treating  bleaching-powder  with  sulphuric  acid. 


REAGENTS.  75 

Bromine  (Br).  Is  a  powerful  and  very  convenient  oxidizing 
agent.  It  is  purchased  in  the  liquid  form,  and  is  generally 
used  as  bromine  water  (water  saturated  with  bromine). 

Potassium  Permanganate  (K2Mn2O8).  Is  a  powerful  oxidiz- 
ing agent,  which  is  largely  used  in  volumetric  analysis.  The 
standard  solutions  are  made  up  as  described  for  the  determina- 
tion of  iron  (Part  II,  Chap.  XVI). 

Potassium  Bichromate  (K2Cr2O,).  Is  a  powerful  oxidizing 
agent,  which  is  largely  used  in  volumetric  analysis.  The  stand- 
ard solutions  are  made  up  as  described  for  the  determination 
of  iron  (Part  II,  Chap.  XVI). 

Nitric  Acid  (HNO3).  Is  a  very  powerful  and  convenient 
oxidizing  agent,  and  is  largely  used  for  the  oxidation  of 
precipitates.  Fuming  nitric  acid  is  the  most  powerful.  It 
should  be  kept  in  a  cool  dark  place  and  should  be  handled 
carefully. 

Potassium  Chlorate  (KC1O3).  Is  a  powerful  oxidizer,  yield- 
ing its  oxygen  with  facility.  Is  largely  used  as  an  oxidizer  in 
fusions  and  for  solutions. 

Sodium  Nitrate  (NaNO3).  Is  largely  used  as  an  oxidizing 
agent  in  fusions.  The  corresponding  potassium  salt  (KNO3) 
may  be  substituted  for  the  sodium  salt. 

Hydrogen  Peroxide  (H2O5).  Is  a  very  powerful  oxidizing 
agent.  The  objection  to  the  use  of  this  reagent  is  the  difficulty 
of  obtaining  it  in  the  pure  state  and  its  liability  to  undergo 
decomposition,  it  soon  losing  its  strength. 

Ammonium  Nitrate  (NH4NO3).  The  salt  is  readily  decom- 
posed upon  heating,  and  is  a  good  oxidizing  agent. 

Indicators. — There  are  a  number  of  color  indicators 
which  are  extremely  useful  in  volumetric  analysis.  These  are 
fully  discussed  in  Chapter  XIII,  AciDIMETRY  AND  ALKALI- 
METRY. 

To  the  above  classes  of  reagents  might  be  added  those 
which  act  as  sulphurizing  and  desulphurizing  agents.  These  are 
mostly  included  in  the  above,  the  principal  sulphurizing  re- 
agents being  sulphur  and  sulphuretted  hydrogen,  and  the  prin- 


?  A   MANUAL    OF  PRACTICAL  ASSAYING. 

cipal  desulphurizing  reagents  used  in  the  wet  way  being  the 
oxidizing  reagents.  In  the  dry  way  the  principal  desul- 
phurizing reagents  have  been  discussed  under  the  head  of 
FLUXES. 

For  a  complete  discussion  of  reagents,  their  preparation, 
etc.,  see  Fresenius'  "  Qualitative  Analysis. ' 


PART  II. 


CHAPTER    I. 
SILICA  (SiOi). 

THE  method  to  be  pursued  in  the  determination  of  silica 
will  depend  on  the  character  of  the  substance  on  which  the 
determination  is  made.  The  following  methods  are  extensively 
used  in  many  of  our  metallurgical  works : 

Iron  Ores. — Most  oxidized  iron  ores  are  decomposed  by 
heating  in  a  beaker  with  concentrated  hydrochloric  acid.  Evap- 
oration to  dryness  is  not  necessary,  and  is  to  be  avoided  except 
where  the  ore  gives  up  gelatinous  silica  on  heating.  When  evap- 
oration to  dryness  is  necessary,  the  evaporation  should  be  finished 
at  comparatively  a  low  temperature,  preferably  on  the  water- 
bath,  otherwise  some  of  the  iron  is  liable  to  be  converted  into  an 
insoluble  form.  After  evaporation  to  dryness  the  mass  is  taken 
up  with  a  small  amount  of  hydrochloric  acid  and  boiled.  It  is 
then  diluted  with  distilled  water  and'  filtered,  transferring  the 
silica  to  the  filter-paper  with  the  successive  additions  of  wash- 
water.  When  the  washings  are  free  from  chloride  of  iron, 
which  can  be  determined  either  by  the  yellow  color  of  the 
filtrate  or  by  testing  with  a  solution  of  ammonium  sulphocy- 
anate,  which  should  turn  red  if  iron  is  present,  a  few  drops  of 
dilute  hydrochloric  acid  are  dropped  around  the  edges  of  the 
filter-paper,  and  the  paper  and  contents  washed  a  few  times 
with  boiling  distilled  water.  This  addition  of  hydrochloric 
acid  to  the  filter-paper  and  subsequent  washings  is  a  precaution 

77 


78  A   MANUAL   OF  PRACTICAL  ASSAYING. 

necessary  to  dissolve  any  trace  of  iron,  calcium  sulphate,  etc., 
which  may  have  remained  on  the  filter  with  the  silica.  The 
filter  and  its  contents  are  then  removed  from  the  funnel,  the 
paper  being  folded  so  as  to  thoroughly  envelop  its  contents. 
It  is  then  placed  in  a  small  porcelain  crucible  and  ignited  in  the 
muffle  furnace  or  over  the  blast-lamp.  Previous  drying  of  the 
paper  and  its  contents  is  unnecessary.  One  gramme  of  the  ore 
is  the  amount  usually  taken.  A  very  convenient  vessel  for  the 
solution  and  evaporation  of  the  ore  is  a  porcelain  casserole,  of 
about  100  cubic  centimetres  capacity,  provided  with  a  handle. 
Some  ore,  such  as  chromic  iron  ore,  and  magnetites  carrying 
considerable  titanium,  will  not  be  thoroughly  decomposed  by 
simple  treatment  with  acids.  In  such  a  case  the  best  method 
of  procedure  is  to  mse  Cn^  insoluble  residue,  after  previous 
ignition,  with  c.  p.  carbonate  of  soda"*  in  a  platinum  crucible, 
one  to  two  grammes  of  carbonate  being  generally  sufficient 
where  one  gramme  of  ore  has  been  taken,  or  the  ore  may  be 
fused  directly  with  sodium  carbonate  and  the  silica  determined 
as  usual  where  a  fusion  is  made. 

The  fusion  can  be  made  over  a  blast-lamp  or  in  the  muffle. 
It  should  be  complete,  which  will  be  indicated  by  the  mass 
being  perfectly  liquid  and  quiet.  Ten  to  twenty  minutes  will 
generally  be  sufficient  time  to  bring  the  fusion  to  completion. 
During  the  last  few  minutes  the  crucible  and  its  contents 
should  be  raised  to  a  high  temperature. 

When  the  fusion  is  complete  the  crucible  is  removed  from  the 
source  of  heat,  and  its  bottom  is  dipped  in  cold  water  in  order 
to  chill  the  mass  quickly.  The  fused  mass  is  removed  from 
the  crucible  by  boiling  water  added  from  a  wash -bottle. 
Slightly  bending  the  crucible  a  few  times  with  the  fingers  will 
greatly  facilitate  the  removal,  and  will  not  injure  the  crucible 
if  proper  care  is  exercised.  The  washings  and  mass  are  poured 
off  into  a  casserole  provided  with  a  convex  glass  cover,  and 
hydrochloric  acid  added  in  slight  excess.  The  solution  is  then 
evaporated  to  dryness,  the  evaporation  being  completed  at 

*  Many  chemists  prefer  a  mixture  of  equal  parts  of  sodium  and  potassium 
carbonate. 


SILICA.  79 

temperature  not  much  above  that  of  boiling  water,  otherwise 
the  mass  is  likely  to  spit,  and  consequently  there  will  be  a  loss. 
The  mass  is  then  heated  at  a  temperature  of  about  120°  C.  until 
all  the  free  hydrochloric  acid  is  driven  off.  It  is  then  taken  up 
with  water  and  a  few  cubic  centimetres  of  hydrochloric  acid, 
boiled,  filtered,  washed,  ignited,  and  weighed. 

Silver-Lead  Ores. — One  gramme  of  ore  is  usually  taken. 
If  the  ore  is  oxidized,  this  is  dissolved  in  seven  cubic  centi- 
metres of  hydrochloric  acid  and  treated  in  the  same  manner  as 
in  the  case  of  iron  ores,  the  precaution  being  taken  to  remove 
the  lead  and  silver  in  the  manner  described  below.  If  the  ore 
is  a  sulphide,  it  is  best  to  dissolve  in  four  cubic  centimetres  of 
strong  hydrochloric  acid,  three  cubic  centimetres  of  strong 
nitric  acid,  and  evaporate  to  dryness. 

It  is  then  taken  up  with  a  few  cubic  centimetres  of  hydro- 
chloric acid,  boiled,  and  diluted  with  distilled  water.  The 
solution  is  then  filtered  off  on  to  a  filter-paper  by  decantation, 
and  after  all  the  chloride  of  iron,  etc.,  is  removed,  about  six  or 
seven  cubic  centimetres  of  a  warm  solution  of  ammonium 
acetate  added  to  the  casserole,  and  its  contents  stirred  with  a 
glass  rod  provided  with  a  rubber  on  the  end.  The  ammonium 
acetate  dissolves  the  sulphate  and  chloride  of  lead  present,  and 
the  stirring  serves  to  break  up  any  clots  of  these  salts  which 
might  not  otherwise  go  into  solution.  Two  additions  of  am- 
monium acetate  are  generally  sufficient  to  dissolve  all  of  the 
lead,  although  a  third  washing  may  sometimes  be  necessary. 

The  ammonium  acetate  is  usually  prepared  as  follows : 
Some  ammonia  is  poured  into  a  beaker,  and  then  acetic  acid  is 
added  until  the  solution  has  an  acid  reaction,  which  is  deter- 
mined by  a  piece  of  litmus-paper.  The  solution  prepared  in 
this  way  is  quite  warm,  owing  to  the  heat  generated  by  the 
combination  of  the  acetic  acid  and  ammonia,  and  is  ready  for 
immediate  use. 

After  all  the  lead  is  removed  the  silver  may  be  removed  by 
treating  with  a  few  drops,  or  cubic  centimetres  if  much  silver 
is  present,  of  ammonia. 

The  insoluble  residue  remaining-  in  the  casserole  is  now 


8O  A   MANUAL   OF  PRACTICAL  ASSA  YING. 

washed  on  the  filter  with  warm  water,  the  filter  washed  once 
more,  and  a  few  drops  of  dilute  hydrochloric  acid  poured 
around  its  edges.  The  filter  and  its  contents  are  now  washed 
again  with  warm  water,  and  are  then  ready  for  ignition  and 
subsequent  weighing. 

For  technical  work  the  insoluble  residue  will  generally  be 
sufficiently  close  to  the  true  amount  of  silica  present  to  be 
considered  as  such.  When  an  ore  contains  silicate  of  alumina  or 
other  insoluble  compounds,  if  an  accurate  determination  is 
required  it  can  be  made  by  fusion  with  sodium  carbonate,  as 
in  the  case  of  iron  ores. 

On  many  ores  a  direct  fusion  of  the  ore  with  acid  sulphate 
of  potassium  (KHSO4)  yields  very  good  results.  To  make 
this  fusion  one  gramme  of  ore  is  mixed  with  five  grammes  of 
potassium  bisulphate  in  a  porcelain  crucible.  The  ore  and 
flux  should  not  fill  the  crucible  much  more  than  one-third  full. 
The  contents  are  then  heated  over  the  flame  of  a  Bunsen 
burner  or  spirit-lamp  until  the  fusion  becomes  quiet.  The 
heat  should  be  low  at  first  in  order  to  prevent  loss  by  rapid 
boiling,  and  should  be  gradually  increased  until  it  is  at  a  dull* 
red.  The  fusion  will  usually  take  about  fifteen  minutes.  When 
it  is  completed  the  crucible  is  removed  from  the  source  of 
heat  and  allowed  to  cool.  When  sufficiently  cool  the  mass  is 
removed  from  the  crucible  by  boiling  water  and  about  thirty 
cubic  centimetres  of  water  added,  and  the  whole  brought 'to  a 
boil  in  order  to  thoroughly  disintegrate  the  mass.  The  solu- 
tion is  then  ready  for  filtration  and  subsequent  ignition,  which 
is  performed  as  before,  more  careful  or  longer  washing  with 
ammonium  acetate  being  required  if  lead  is  present,  as  the 
lead  is  all  in  the  form  of  sulphate. 

Slags. — In  the  case  of  lead  slags  the  method  to  be  pursued 
will  depend  on  the  manner  in  which  the  sample  was  taken.  If 
the  sample  was  taken  on  a  rod*  and  chilled  suddenly  the  silica 
maybe  determined  by  treating  half  a  gramme  in  a  small  casse- 
role of  about  100  cubic  centimetres  capacity,  with  about  two 

*  See  Part  I,  page  18. 


SILICA.  8 I 

cubic  centimetres  of  water,  and  stirring  with  a  glass  rod,  then 
adding  two  or  three  cubic  centimetres  of  strong  hydrochloric 
acid  and  stirring  again.  This  addition  of  water  and  stirring 
prevents  the  slag  coagulating  and  sticking  to  the  bottom  of  the 
casserole,  which  it  would  otherwise  do,  and  consequently  would 
be  difficult  to  decompose.  A  few  drops  of  strong  nitric  acid  are 
now  added,  the  casserole  being  covered  with  a  convex  glass  to 
prevent  loss  by  effervescence,  and  the  contents  stirred  again. 
Sufficient  nitric  acid  should  be  added  to  decompose  whatever  sul- 
phides are  present  and  oxidize  the  iron,  leaving  a  slight  excess  of 
nitric  acid  in  solution.  A  considerable  excess  of  acid  is  to  be 
avoided,  as  this  would  only  prolong  the  evaporation,  and  cause 
loss  of  time.  The  mass  is  then  evaporated  to  dryness,  care 
being  taken  not  to  raise  to  such  a  temperature  as  to  cause 
the  gelatinous  silica  to  spit.  The  subsequent  driving  off  of 
the  free  hydrochloric  acid  may  be  facilitated  by  breaking  up 
the  lumps  with  a  glass  rod,  and  also  by  moistening  with  a  few 
drops  of  water  once  or  twice,  and  heating  to  dryness  again. 
It  is  essential  that  all  of  the  free  acid  and  water  should  be  driven 
off,  in  order  that  all  of  the  silica  may  be  rendered  insoluble. 
After  the  first  evaporation  to  dryness  the  casserole  can  be  re- 
moved to  a  warmer  place,  care  being  taken  not  to  heat  to  such 
a  degree  that  the  iron  will  be  rendered  insoluble.  If  iron  is  to 
be  determined  in  the  filtrate  from  the  silica,  the  mass  should 
not  be  heated  to  a  temperature  much  over  110°  C.,  as  chloride 
of  iron  is  volatile  at  quite  a  low  temperature.  After  the  free 
hydrochloric  acid  is  driven  off  the  casserole  is  removed  from 
the  source  of  heat,  and  the  mass  moistened  with  a  little  water, 
and  about  two  cubic  centimetres  of  hydrochloric  acid  added. 
The  contents  of  the  casserole  are  then  brought  to  a  boil. 
After  diluting  with  water  the  silica  can  be  filtered  off,  dried, 
ignited,  and  weighed,  as  in  the  case  of  silver-lead  ores. 

The  silica  should  be  white,  and  there  should  be  no  gritty 
particles  in  the  bottom  of  the  casserole  after  solution.  In  the 
analysis  of  something  over  a  thousand  different  samples  of  lead 
blast-furnace  slags  the  writer  has  never  yet  encountered  a  slag 
which  did  not  yield  to  this  method  of  treatment,  except  in  the 


82  A   MANUAL   OF  PRACTICAL  ASSAYING. 

case  of  slags  containing  barium.  If  the  slags  contain  barium, 
some  sulphate  of  barium,  which  is  insoluble,  will  invariably  be 
formed  when  the  sulphides  are  oxidized  with  the  nitric  acid, 
and  be  precipitated  with  the  silica. 

This  method  of  decomposing  lead  slags  has  been  tested  by 
the  writer  and  others,  a  number  of  times,  by  fusing  the  insol- 
uble residue,  obtained  as  above,  with  carbonate  of  soda,  and 
determining  the  silica  in  the  regular  manner,  with  results 
agreeing  so  closely  with  those  obtained  by  weighing  the  in- 
soluble residue  as  to  prove  the  accuracy  of  the  method — at 
least  for  all  technical  purposes. 

A  determination  may  be  made  in  this  way  in  less  than  forty 
minutes.  In  case  the  slag  contains  barium,  a  good  method  of 
procedure  is  to  weigh  the  insoluble  residue,  and  fuse  it  with 
about  a  gramme  and  a  half  of  carbonate  of  soda  in  a  platinum 
crucible.  The  fused  mass  is  then  removed  from  the  crucible, 
and  dissolved  in  water  by  boiling.  It  is  then  filtered  through 
a  small  filter,  and  washed  thoroughly  with  warm  water  to 
remove  all  the  silicate  and  sulphate  of  sodium.  This  can  be 
determined  by  acidifying  the  washings  with  a  few  drops  of 
hydrochloric  acid,  heating,  and  adding  a  few  drops  of  barium- 
chloride  solution.  The  carbonate  of  barium  is  then  dissolved 
on  the  filter-paper  with  dilute  hydrochloric  acid,  and  several 
subsequent  washings  with  warm  water  into  a  clean  beaker, 
and  after  bringing  the  solution  to  a  boil  the  barium  is  precipi- 
tated by  the  addition  of  a  few  drops  of  sulphuric  acid,  and  de- 
termined as  barium  sulphate,  as  described  in  Part  II,  Chapter 
XXV. 

The  weight  of  the  barium  sulphate  thus  determined  may 
be  deducted  from  the  weight  of  the  insoluble  residue,  the  dif- 
ference being  considered  as  silica.  This  determination  of  the 
silica  by  difference  is  generally  considered  sufficiently  accurate. 
If  greater  refinement  is  necessary,  the  silica  may  be  determined 
directly  in  the  filtrate  by  acidifying  with  hydrochloric  acid, 
and  evaporating  to  dryness,  as  in  the  case  of  an  ordinary 
fusion  for  silica.  This  evaporation  takes  considerable  time  on 
account  of  the  bulk  of  the  liquid,  and  liability  to  loss  through 


SILICA.  83 

spitting,  unless  the  evaporation  takes  place  slowly.  (See 
determination  of  silica  in  slags,  etc.)  An  excellent  method 
for  technical  purposes  is  described  in  Chapter  XXV,  page 
225. 

The  same  method  may  be  used  for  the  determination  of 
silica  in  ores  containing  barium  sulphate.  The  chemist  will 
sometimes  be  called  upon  to  analyze  slags  where  the  sample 
has  not  been  taken  in  the  manner  described,  as,  for  example,  a 
piece  of  lump  slag  broken  from  a  cold  pot  or  cone.  In  this 
case  the  slag  will  very  rarely  be  decomposed  by  direct  treat- 
ment with  acids.  A  direct  fusion  of  the  slag  in  platinum  is  not 
safe,  as  there  is  a  liability  of  the  lead,  which  the  slag  contains, 
attacking  the  crucible.  This  difficulty  can  generally  be  obvi- 
ated in  the  following  manner :  Mix  one  half  a  gramme  of  the 
slag  with  about  one  and  a  half  grammes  of  sodium  carbonate, 
and  transfer  to  a  small  platinum  dish  (of  about  25  cc.  capacity). 
Place  in  the  muffle,  and  heat  till  the  mass  cinters  together, 
care  being  exercised  not  to  heat  sufficiently  long  or  to  a  suffi- 
ciently high  temperature  to  fuse  the  mass,  or  else  the  lead  is 
liable  to  be  reduced  and  injure  the  platinum.  As  soon  as  the 
mass  has  cintered,  remove  from  the  muffle  and  cool.  If  the 
cintering  has  been  properly  performed  the  mass  will  almost 
invariably  be  decomposed  by  the  addition  of  water  and  hydro- 
chloric and  nitric  acids,  when  the  silica  may  be  determined  in 
the  manner  described  above.  A  platinum  crucible  may  be 
used  in  place  of  a  dish,  but  a  dish  is  preferable,  inasmuch  as  if 
a  crucible  is  used  the  mass  is  liable  to  fuse  around  the  edges 
before  it  has  begun  to  cinter.  When  barium  is  present  fuse 
the  insoluble  residue  as  before. 

Iron  Blast-furnace  Slags. — The  first  method  described 
above  does  very  well  for  the  determination  of  these  slags  for 
technical  purposes,  the  sample  when  taken  being  suddenly 
chilled.  According  to  some  authors,  the  decomposition  is  not 
as  good  as  in  the  case  of  lead-slags,  but  from  all  the  results 
which  the  author  has  seen  he  would  say  that  they  were 
sufficiently  close  to  check  the  workings  of  the  furnace,  for 
which  the  determinations  are  usually  made.  When  the  sample 


84  A   MANUAL   OF  PRACTICAL  ASSAYING. 

has  not  been  suddenly  chilled  on  taking,  the  best  method  is  to 
fuse  one  half  a  gramme  of  finely  pulverized  slag  with  about 
three  grammes  of  sodium  carbonate.  Remove  fused  mass 
from  the  crucible,  and  determine  as  in  the  case  of  fusion  of 
iron  ores. 

Copper-furnace  Slags. — These  may  be  treated  in  the 
same  manner  as  lead  slags. 

Fused  Ore. — This  may  be  sampled  and  treated  in  the 
same  way  as  lead  slags.  Whether  the  chilled  sample  of  ore 
will  be  decomposed  in  acids  or  not,  depends  upon  its  composi- 
tion and  the  completeness  of  the  fusion  before  the  ore  was 
drawn  from  the  furnace.  Very  frequently  it  will  not  decom- 
pose. Under  these  circumstances,  the  insoluble  residue  which 
is  free  from  lead,  must  be  fused  with  sodium  carbonate  and 
the  silica  determined  as  before. 

Mattes.  —  These  will  seldom  decompose  completely  in 
acids,  owing  to  the  slag  which  is  mixed  with  them  mechani- 
cally. Generally  the  insoluble  residue  will  have  to  be  fused 
with  sodium  carbonate  if  an  accurate  silica  determination  is 
required. 

Limestones. — As  the  silica  of  most  limestones  is  present 
in  the  form  of  slate  or  quartz,  the  insoluble  residue  will  gener- 
ally represent  the  amount  of  silica  present.  The  limestone 
should  be  dissolved  in  hydrochloric  acid,  using  about  6  to  7 
cc.  of  acid  for  I  gramme  of  limestone, — the  amount  generally 
taken, — and  a  few  drops  of  nitric  acid  to  decompose  any  pyrite 
that  maybe  present.  In  the  case  of  a  limestone  carrying  clay, 
the  insoluble  residue  will  have  to  be  fused  with  sodium  carbon- 
ate, as  above. 

Fire-clays,  Marls,  etc. — As  these  substances  contain  sili- 
cate of  alumina,  which  is  not  decomposed  by  acids,  I  gramme 
of  the  substance  is  fused  direct  with  about  5  or  6  grammes  of 
carbonate  of  soda,  and  the  silica  determined  as  usual.  When 
the  alumina  is  also  to  be  determined,  the  insoluble  residue  can 
first  be  determined  by  evaporation  with  acids,  as  in  the  case 
of  iron  ores.  The  silica  is  then  determined  by  fusion  with 
sodium  carbonate  as  before,  the  difference  between  the  per- 


SILICA.  85 

centage  of  silica  and  the  percentage  of  insoluble  residue  being 
the  percentage  of  alumina  (A13O3).  When  barium  is  present, 
the  method  of  procedure  after  fusion  of  the  insoluble  residue 
is  the  same  as  in  the  case  of  the  determination  of  silica  in  lead 
slags  containing  barium. 

Note. — In  nearly  all  cases  where  an  ore  or  product  does 
not  contain  lead  and  a  fusion  is  necessary  to  decompose  it,  the 
fusion  may  be  made  directly,  thus  frequently  saving  time. 
Where  an  ore  is  known  to  contain  silicate  of  alumina,  and  the 
alumina  is  to  be  determined,  it  is  best  to  obtain  the  insoluble 
residue,  weigh  it,  and  then  fuse,  determining  the  silica  as 
before  and  the  alumina  by  difference,  or  directly  in  the  filtrate, 
from  the  silica. 

Pig-iron,  Steel,  etc. — The  following  method,  proposed  by 
Dr.  Drown,*  for  the  determination  of  silicon  in  pig-iron,  etc., 
is  used  in  some  of  our  largest  metallurgical  works,  and  is  as 
accurate  and  rapid  as  any : 

Treat  I  gramme  of  finely  pulverized  iron  or  steel  in  a  cov- 
ered casserole  with  10  cc.  of  water  and  about  8  cc.  of  concen- 
trated nitric  acid,  until  action  ceases.  Add  4  cc.  of  sulphuric 
acid  and  heat  on  an  iron  plate  or  sand-bath  until  the  nitric 
acid  is  all  expelled.  This  evaporation  can  be  facilitated  by 
conducting  it  in  a  platinum  dish  with  a  strong-flamed  Bunsen 
burner  below  and  another  from  a  blast-lamp  above,  the  latter 
flame  being  directed  downward  upon  the  surface  of  the  solu- 
tion in  the  dish. 

When  the  evaporation  is  complete,  which  will  be  indicated 
by  dense  white  fumes  of  sulphuric  anhydride,  the  silica  will 
all  be  insoluble.  Remove  from  the  source  of  heat  and  cool. 
When  the  contents  of  the  dish  are  cold,  add  cold  water,  about 
40  cc.,  carefully,  to  prevent  spitting,  and  a  few  cubic  centi- 
metres of  hydrochloric  acid.  Heat,  filter,  wash,  ignite,  and 
weigh  as  usual.  The  addition  of  considerable  water  and 
hydrochloric  acid  is  necessary  to  dissolve  the  ferrous  sulphate 
formed  during  evaporation.  After  the  silica  is  transferred  to 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  Vol.  VII,. 
p.  346. 


86  A   MANUAL    OF  PRACTICAL   ASSAYING. 

the  filter,  it  should  be  thoroughly  washed  with  hot  water  and 
hydrochloric  acid,  as  in  iron  ores.  In  the  case  of  ferro-silicons 
where  the  percentage  of  silicon  is  high,  this  treatment  with 
acids  will  fail,  except  by  repeated  additions  of  fresh  acid  and 
repeated  evaporations.  In  this  case  a  shorter  method  is  to 
fuse  I  gramme  of  the  pulverized  metal  with  sodium  carbonate 
in  a  covered  platinum  crucible.  The  silicon  is  converted  into 
a  sodium  silicate  and  the  spongy  iron  remains  in  a  finely- 
divided  condition,  and  is  readily  attacked  by  acids.  After 
fusion  is  complete,  remove  from  heat,  cool,  and  dissolve  in 
hot  water  and  hydrochloric  acid.  Evaporate  to  dryness,  and 
determine  silica  as  in  fusion  of  iron  ores. 

The  silicon  is  determined  as  silica  and  weighed  as  such. 
From  the  weight  of  the  silica  calculate  the  percentage  of  sili- 
con as  follows  :  Multiply  the  weight  of  the  silica  found  by  7 
and  divide  the  result  by  15  ;  the  quotient  will  be  the  weight 
of  the  silicon  in  the  amount  of  substance  taken. 

Note. — The  purity  of  silica  can  always  be  tested  in  the 
following  manner  :  Brush  the  insoluble  residue  into  a  weighed 
platinum  crucible,  moisten  with  pure  concentrated  sulphuric 
acid,  and  add  one  gramme  of  ammonium  fluoride.  Place  the 
lid  on  the  crucible  and  incline  it  in  its  support ;  then  heat 
gently  by  a  burner  or  spirit-lamp,  allowing  the  flame  to  play 
around  the  top  of  the  crucible.  Continue  this  heating  (it 
should  always  be  performed  under  a  hood  with  a  good  draught) 
until  all  the  sulphuric  acid  is  expelled.  Then  heat  the  crucible 
strongly,  removing  the  cover  towards  the  last  of  the  operation, 
cool  and  weigh  the  crucible,  and  repeat  the  operation,  if  nec- 
essary, until  the  crucible  ceases  to  lose  weight.  The  loss  in 
weight  represents  the  silica  expelled  as  silicon  fluoride,  and  if 
the  silica  as  previously  determined  was  pure,  should  equal  its 
weight.  Whatever  remains  in  the  crucible,  if  anything,  may 
be  alumina,  barium  sulphate,  ferric  oxide,  etc.  If  these  con- 
stituents are  to  be  determined,  they  may  be  obtained  in 
solution,  with  the  exception  of  barium,  by  fusing  with  acid 
potassium  sulphate. 

Titaniferous  Ores. — Many  iron  ores,  especially  magnetites, 


SILICA.  87 

contain  considerable  quantities  of  titanium.  None  of  the 
above  methods  will  serve  to  thoroughly  decompose  such  ores. 
The  following  method,  proposed  by  Dr.  Drown,*  is  in  general 
use:  Fuse  I  gramme  of  ore  in  a  platinum  crucible  with  sodium 
carbonate.  Dissolve  in  warm  water  and  hydrochloric  acid, 
arid  after  solution  is  effected  add  an  excess  of  sulphuric  acid 
(40  cc.)  and  evaporate  until  all  the  hydrochloric  acid  is  driven 
off,  thus  rendering  the  silica  insoluble.  Dissolve  the  ferrous 
sulphate  in  water  and  hydrochloric  acid,  heat  to  effect  solution, 
filter,  wash  with  warm  water  and  hydrochloric  acid,  ignite,  and 
weigh  the  silica. 

Note. — The  best  Swedish  and  German  filter-papers,  such 
as  Schleicher  &  Schuell's  c.  p.  paper,  leave  such  a  small  quan- 
tity of  ash  after  ignition  that  the  weight  of  the  filter-ash  may 
be  disregarded  when  this  paper  is  used.  Should  pure  filter- 
paper  not  be  at  hand,  the  ash  of  the  paper  should  be  deter- 
mined as  follows  :  Place  about  six  pieces  of  the  paper  to  be 
used  in  a  glass  funnel,  and  wash  with  warm  water  containing 
several  cubic  centimetres  of  hydrochloric  acid.  After  washing, 
roll  the  paper  together,  place  in  a  crucible,  dry,  ignite,  and 
weigh.  From  the  total  weight  calculate  the  weight  of  one 
piece  of  paper.  The  weight  thus  obtained  should  be  deducted 
from  the  combined  weights  of  the  silica  and  filter-ash  in  each 
determination. 

Bauxite. — As  this  mineral  frequently  contains  titaniun,  a 
method  for  its  separation  must  be  adopted  in  determining  the 
value  of  an  ore  and  its  silica  contents.  Fuse  0.5  gm.  of  the 
finely  pulverized  mineral  with  potassium  bisulphate  in  a  cov- 
ered platinum  crucible.  Dissolve  the  fused  mass  in  hot  water, 
filter,  wash,  dry,  ignite,  and  weigh.  Treat  this  residue  with 
hydrofluoric  acid,  and  should  a  residue  remain  after  expelling 
the  silica,  weigh  it  and  deduct  this  weight  from  the  weight  of 
the  insoluble  residue  as  obtained,  the  difference  being  the 
weight  of  the  silica,  f 

*  Transactions  of  the  American   Institute  of  Mining  Engineers,    Vol.  X, 

P.  143- 

f  Mineral  Resources  of  the  U.  S.  1892.     Washington,  1893. 


CHAPTER  II. 

SULPHUR  (S). 

WHILST  there  are  a  great  many  methods  in  use  for  the  de- 
termination of  sulphur  in  ores,  furnace  products,  etc.,  the  author 
must  confess,  after  having  tried  a  great  number  of  different 
methods,  that  he  has  not  as  yet  found  a  method  which  is  accu- 
rate and  at  the  same  time  rapid. 

Fahlberg-Iles'  Modified  Method. — This  method  was  first 
proposed  by  M.  W.  lies*  for  the  determination  of  sulphur  in 
certain  organic  compounds  which  are  extremely  difficult  to 
decompose  by  ordinary  means,  such  as  treatment  with  acids  or 
an  ordinary  fusion.  It  consists  in  decomposing  the  substances 
by  fusion  with  caustic  alkali,  subsequent  solution  of  the  fused 
mass  in  water,  oxidation  of  the  sulphur,  and  determination  as 
barium  sulphate.  The  method  is  largely  used  for  the  determi- 
nation of  sulphur  in  ores  and  furnace  products, f  and  is  accurate 
if  the  precaution  is  taken  to  remove  all  of  the  silica  which  the 
solution  may  contain  before  addition  of  the  barium  solution. 
This  is  a  precaution  which  is  not  mentioned  by  the  author  of 
this  method  or  by  any  of  the  text-books,  but  is  a  precaution 
which  the  writer  has  found  by  numerous  experiments  to  be 
essential,  owing  to  the  fact  that  if  the  silica  is  not  removed  a 
large  portion  of  it  will  be  precipitated  together  with  the  barium 
sulphate  and  be  weighed  as  such.  The  method  as  modified  by 
the  writer  is  as  follows  : 

Fuse  i.o  gramme  of  substance  with  from  one  to  two  sticks 
of  potassium  hydrate  (the  c.  p.  caustic  potash  by  alcohol  should 

*  School  of  Mines  Quarterly;  American  Chemical  Journal;  etc. 
f  School  of  Mines  Quarterly. 

88 


SULPHUR.  89 

be  used,  as  any  other  generally  contains  sulphur.  It  should 
always  be  tested  for  sulphur,  to  be  sure  that  it  contains  none) 
in  a  silver  crucible  (a  crucible  lined  with  gold  is  preferable,  as 
the  alkali  generally  attacks  the  silver  of  the  crucible  to  a  slight 
extent)  over  a  spirit-lamp.  The  best  method  of  making  the 
fusion  is  to  place  the  potassium  hydrate  in  the  crucible  and 
heat  over  the  spirit-lamp  (gas  cannot  be  used,  as  it  always  con- 
tains sulphur  compounds)  to  quiet  fusion.  Then  remove  the 
lamp  from  underneath  the  crucible,  brush  the  substance  into  it, 
and  heat  for  from  5  to  30  minutes  until  the  substance  is 
thoroughly  decomposed.  Remove  the  crucible  and  allow  it  to 
cool ;  as  soon  as  cold  dissolve  the  mass  out  with  warm  water 
into  a  beaker,  and  when  it  is  all  transferred  to  the  beaker  bring 
its  contents  to  a  boil  and  filter  through  a  ribber  filter-paper. 
Wash  with  boiling  water  until  the  washings  come  through  free 
from  sulphides  or  sulphates.  Add  from  20  cc.  to  40  cc.  of 
bromine  water  to  the  filtrate  and  heat  to  about  90  degrees  C., 
and  then  acidify  with  hydrochloric  acid.  If  the  substance  con- 
tains silica,  it  will  now  be  in  solution,  and  must  be  removed  by 
evaporating  the  solution  to  dryness,  heating  and  dissolving 
with  water  and  hydrochloric  acid,  and  filtering  off  the  silica  thus 
rendered  insoluble.  (See  Chapter  I.) 

To  the  filtrate  from  the  silica,  after  boiling,  add  a  solution 
of  boiling  barium  chloride  until  all  of  the  sulphur  is  precipitated 
as  barium  sulphate.  By  heating  the  solution  of  barium  chlo- 
ride, before  adding  it  to  the  solution,  the  barium  sulphate  is 
precipitated  almost  immediately,  which  is  not  the  case  if  a  cold 
solution  of  barium  salt  is  used.  After  the  addition  of  the 
barium  chloride  the  solution  is  brought  to  a  boil  and  then  re- 
moved to  a  warm  place  and  allowed  to  settle.  After  settling, 
it  is  filtered,  washed  thoroughly  with  boiling  water,  and  then 
with  a  few  drops  of  dilute  hydrochloric  acid  dropped  around 
the  edge  of  the  paper  and  again  twice  with  hot  water.  It 
should  be  washed  until  the  washings  no  longer  give  a  precipi- 
tate with  silver-nitrate  solution. 

The  precipitate  is  now  dried,  together  with  the  filter-paper, 
and  when  dry  transferred  to  a  crucible  by  inverting  the  filter- 


9O  A   MANUAL   OF  PRACTICAL  ASSAYING. 

paper  in  the  crucible  and  gently  rolling  in  the  fingers.  (See 
Chapter  XXV,  Barium.)  The  crucible  should  be  placed  on  a 
large  clean  watch-glass  so  that  any  particles  which  may  fly  out- 
side of  the  crucible  can  be  recovered.  After  all  that  is  possi- 
ble is  removed  from  the  filter-paper,  it  is  rolled  up  and 
placed  on  the  lid  of  a  platinum  crucible  and  burned  by 
holding  the  platinum  over  the  flame  of  a  burner  or  spirit-lamp. 
The  ash  of  the  filter-paper  is  then  added  to  the  contents  of  the 
crucible,  and  the  whole  ignited  in  the  muffle  or  over  the  blast- 
lamp.  The  crucible  is  then  cooled  and  its  contents  should  be 
found  perfectly  white.  The  precipitate  is  now  transferred  from 
the  crucible  to  the  watch-glass  of  the  balance  and  weighed. 
The  weight  of  the  barium  sulphate,  less  the  known  weight  of 
the  filter-ash,  multiplied  by  0.13734,  will  be  the  weight  of  the 
sulphur  present  in  the  amount  of  substance  taken. 

When  silica  is  not  present  the  evaporation  to  dryness  of  the 
filtrate  from  the  solution  of  the  fusion  can  be  omitted,  thus 
greatly  shortening  the  method.  This  method  is  universal  in  its 
application,  but  unfortunately  requires  considerable  time,  ow- 
ing to  the  time  required  to  evaporate  the  solution  to  dryness, 
and  drive  off  the  free  hydrochloric  acid  for  the  precipitation  of 
the  silica,  which  must  be  conducted  slowly  on  account  of  the 
large  amount  of  salts  present.  When  evaporation  to  dryness 
is  not  necessary,  a  determination  may  be  made  in  less  than  an 
hour  and  a  half. 

Second  Method. — The  following  method  is  frequently  used 
in  lead-  and  copper-smelting  works  for  the  determination  of 
sulphur,  and  whilst  it  is  not  as  accurate  as  the  method  pre- 
viously described,  it  has  the  advantage  of  being  rapid,  and  con- 
sequently would  be  used  where  time  for  an  accurate  determina- 
tion is  not  available  : 

Treat  one  gramme  of  ore  in  a  flask  (about  200  cc.  capacity) 
with  three  to  four  grammes  of  potassium  chlorate  and  7  cc.  of 
nitric  acid,  the  acid  being  added  as  follows  :  About  3  cc.  at 
first,  and  then  I  cc.  from  time  to  time.  When  all  the  acid 
has  been  added,  heat  to  boiling  on  a  sand-bath  and  evaporate 
off  the  excess  of  acid.  All  but  about  2  cc.  of  acid  should  be 


SULPHUR.  91 


expelled.  The  potassium  chlorate  and  nitric  acid  oxidize  the 
sulphur  in  the  ore,  and  in  the  case  of  a  heavy  sulphide  more 
potassium  chlorate  may  be  necessary.  The  solution,  after 
boiling,  should  show  no  undecomposed  particles  of  sulphides 
and  no  globules  of  yellow  sulphur,  which  will  sometimes  form 
if  the  oxidation  has  been  imperfect.  Remove  from  the  source 
of  heat,  dilute  with  about  50  cc.  of  water,  and  add  a  saturated 
solution  of  sodium  carbonate  in  excess.  The  sodium  carbonate 
precipitates  the  lead,  iron,  etc.,  and  the  excess  is  added  to 
decompose  the  sulphates  of  lead  and  calcium  which  may  have 
formed  during  solution.  Boil  for  from  thirty  minutes  to  one 
hour,  adding  water  from  time  to  time  to  keep  the  bulk  of  the 
solution  about  the  same.  Filter  through  a  fluted  filter  into  a 
beaker,  and  wash  until  the  washings  no  longer  show  the  pres- 
ence of  sulphuric  acid.  Acidify  the  filtrate  with  hydrochloric 
acid,  and  boil  to  expel  the  carbonic  acid.  When  the  carbonic 
acid  is  all  expelled  the  solution  is  ready  for  the  precipitation 
of  the  sulphuric  acid  with  barium-chloride  solution,  and  the 
determination  of  the  barium  sulphate  as  before.  If  the  ore 
contains  barium  sulphate  it  will  remain  undecomposed  with  the 
precipitate  of  mixed  carbonates. 

Matte  Fusion.  —  The  writer  has  frequently  had  occasion  to 
make  use  of  this  method  to  obtain  data  upon  which  to  calcu- 
late a  furnace  charge  when  time  was  wanting  in  which  to  make 
an  accurate  sulphur  determination. 

This  assay  is  made  in  order  to  determine  the  amount  of 
sulphur,  or  matte-forming  material,  which  an  ore  contains.  It 
is  at  best  only  an  approximation,  but  generally  gives  a  result 
which  is  a  sufficiently  close  approximation  to  the  actual  amount 
of  matte  which  an  ore  will  produce  in  the  blast-furnace  to  be 
of  value  for  metallurgical  purposes.  It  has  the  advantage  of 
being  a  rapid  method,  which  is  frequently  of  the  utmost  impor- 
tance in  a  smelting-works.  This  method  takes  about  20 
minutes,  whilst  a  sulphur  determination  in  the  wet  way,  even 
within  reasonably  close  limits,  cannot  be  made  in  much  less 
than  an  hour  and  a  quarter. 


92  A   MANUAL    OF  PRACTICAL  ASSAYING. 

A  charge  which  will  generally  give  very  good  results  is  as 
follows : 

Ore 5  grammes. 

Borax  glass 15         " 

Charcoal 3 

One  or  two  nails,  points  down. 

The  charge  is  thoroughly  mixed  in  an  ordinary  clay  cruci- 
ble and  placed  in  the  furnace,  the  time  of  fusion  with  a  hot  fire 
being  about  15  minutes.  After  the  fusion  is  complete  the 
crucible  is  removed  from  the  furnace,  the  nails  drawn  out,  and 
the  assay  poured.  As  soon  as  the  cone  is  cool  it  is  removed 
from  the  mould  and  the  slag  broken  off  from  the  matte  button, 
which  is  then  weighed  and  the  percentage  calculated.  In  the 
case  of  a  lead  ore  a  lead  button  will  also  be  found  below  the 
matte,  but  this  is  easily  separated  from  the  matte  button.  The 
matte  button  may  be  generally  considered  as  containing  about 
30  per  cent  sulphur,  although  the  amount  of  sulphur  which  it 
will  contain  will  vary  somewhat,  according  to  the  nature  of  the 
ore.  Theoretically  the  button  should  contain  36.3  per  cent 
sulphur,  matte  being  considered  as  FeS.  However,  a  pure 
matte  is  seldom  produced,  as  the  ores  generally  contain  impuri- 
ties such  as  zinc,  copper,  lead,  arsenic,  antimony,  etc.  A  num- 
ber of  analyses  of  matte  buttons  produced  in  this  way  show 
that  an  average  of  30  per  cent  sulphur  is  reasonably  close. 

Volumetric  Method. — The  following  volumetric  method 
was  suggested  by  Alexander's  method  for  the  determination 
of  lead  (see  Part.  II,  Chapter  VIII).  The  method  requires  a 
standard  solution  of  ammonium  molybdate,  which  is  prepared 
by  dissolving  30.7  gms.  of  ammonium  molybdate  in  water  and 
diluting  to  1000  cc.  Each  cc.  of  this  solution  should  be  equiv- 
alent to  0.005  gm.  of  sulphur.  To  standardize  the  solution 
weigh  out  two  portions  of  from  0.3  to  0.5  gm.  of  pure  sheet 
lead,  dissolve  in  a  few  cc.  of  dilute  nitric  acid,  add  a  slight 
excess  of  sulphuric  acid,  and  boil  to  drive  off  the  nitric  acid. 
Cool,  add  a  slight  excess  of  ammonia,  and  then  strong  acetic 


SULPHUR.  93 

acid  in  excess.  Heat  to  dissolve  the  lead  sulphate  and  dilute 
with  hot  water  to  about  1 80  cc.,  when  the  solution  is  ready  for 
titration  with  the  molybdate  solution.  The  molybdate  solu- 
tion is  run  in  from  a  burette  with  constant  stirring,  and  a  drop 
of  the  solution  tested  from  time  to  time  on  a  porcelain  plate 
with  a  drop  of  a  solution  of  tannin.  As  soon  as  the  molybdate 
solution  is  in  slight  excess  the  drop  of  the  solution  added  to  the 
tannin  solution  will  turn  it  yellow,  when  the  titration  is  finished. 
From  the  amount  of  lead  taken  and  the  number  of  cc.  of 
molybdate  solution  used,  the  value  of  the  solution  in  terms  of 
sulphur  may  be  calculated  as  follows  :  Suppose  0.3  gm.  of  lead 
was  taken  and  10  cc.  of  molybdate  solution  was  used  to  pre- 
cipitate the  lead.  Then  I  cc.  of  molybdate  solution  is  equiv- 
alent to  0.03 'gm.  of  lead,  or  to  0.043913  gm.  of  lead  sulphate, 
and  as  lead  sulphate  contains  10.56  per  cent  sulphur,  its  equiv- 
alent in  S  may  be  calculated  by  the  factor  0.1056  ;  the  equiv- 
alent in  this  case  being  I  cc.  —  0.004637  -]-• 

To  determine  sulphur  in  an  ore  or  metallurgical  product  by 
this  method  the  ore  may  be  decomposed  and  the  sulphur 
obtained  irw  solution  by  fusion  with  caustic  potash  as  described, 
by  treatment  with  nitric  acid  and  chlorate  of  potash  and 
subsequent  treatment  with  sodium  carbonate  as  described,  or 
by  fusion  in  a  porcelain  or  platinum  crucible  with  a  mixture 
of  sodium  carbonate  and  potassium  nitrate. 

Where  fusion  with  caustic  potash  is  the  method  employed 
the  fused  mass  is  dissolved  in  hot  water  and  filtered,  hydrogen 
peroxide  being  added  to  the  filtrate  to  oxidize  the  potassium 
sulphide.  The  solution  is  then  heated  and  acidified  with  a 
slight  excess  of  nitric  acid.  To  the  hot  solution  add  an  excess 
of  a  solution  of  lead  nitrate,  allow  to  stand  until  the  precipi- 
tated lead  sulphate  "settles  and  filter,  retaining  as  much  as 
possible  of  the  lead  sulphate  in  the  beaker.  Wash  by  decanta- 
tion  with  cold  water  until  the  washings  no  longer  give  a  reac- 
tion for  lead.  •  Dissolve  the  lead  sulphate  in  hot  ammonium 
acetate,  acidify  with  acetic  acid  and  titrate  with  the  standard 
ammonium  molybdate  solution. 

In  case  the  nitric  acid-potassium   chlorate  method  is  used, 


94  A    MANUAL    OF  PRACTICAL  ASSAYING. 

acidify  the  filtrate  from  the  precipitated  carbonates  with  a 
slight  excess  of  nitric  acid,  boil  out  the  carbonic  acid,  pre- 
cipitate the  sulphuric  acid  with  lead  nitrate,  and  proceed  as 
above. 

In  case  fusion  with  mixed  carbonate  of  soda  and  potassium 
nitrate  is  the  method  adopted,  to  each  gramme  of  substance 
taken  add  about  10  gms.  of  the  mixed  salts  and  fuse  until  the 
mass  is  liquid.  Cool  and  dissolve  the  fused  mass  in  hot  water. 
Filter,  acidify  the  filtrate  with  nitric  acid,  boil  to  drive  out 
carbonic  acid,  precipitate  the  sulphuric  acid  with  lead  nitrate, 
and  proceed  as  above. 

In  all  cases  the  reagents  used  should  be  examined  for 
sulphur,  as  they  are  liable  to  contain  sulphates.  If  pure  re- 
agents cannot  be  obtained  a  blank  analysis  should  be  run,  using 
the  same  quantity  of  reagents  as  in  the  regular  analysis,  and 
deducting  the  amount  of  sulphur  found  in  the  blank  analysis 
from  that  found  in  the  regular  analysis. 

In  the  case  of  ores,  etc.,  containing  but  a  small  percentage 
of  sulphur,  it  is  advisable  to  use  a  more  dilute  solution  of 
ammonium  molybdate.  Having  made  up  the  solution  and 
standardized  it  as  described,  a  solution  of  any  desired  strength 
can  be  readily  prepared  by  drawing  off  a  definite  quantity  of 
the  standardized  solution  and  diluting  it  with  water  to  any 
desired  strength. 

Iron  and  Steel. — The  following  rapid  method  for  the 
determination  of  sulphur  in  iron  and  steel  is  quite  accurate, 
and  is  extensively  used  in  metallurgical  works  for  technical 
determinations.  Many  modifications  of  the  method  have  been 
proposed,  but  the  two  following  are  believed  to  be  as  good  and 
rapid  as  any.  The  method  was  originally  suggested  by  Kar- 
sten,  and  depends  upon  the  principle  that,  if  iron  or  steel  is 
dissolved  in  dilute  hydrochloric  or  sulphuric  acid,  H2S  is 
evolved.  The  evolved  H2S  may  subsequently  be  absorbed  in 
a  solution  of  a  metallic  salt. 

The  cut,  Fig.  13,  shows  the  usual  arrangement  of  appara- 
tus for  carrying  out  the  decomposition  and  absorption.  The 
wash  bottle  A  contains  an  alkaline  solution  of  lead  nitrate. 


SULPHUR. 


95 


The  generator  G  is  used  for  generating  hydrogen  gas.  The  fun- 
nel-tube C  is  tightly  connected  with  A.  The  small  flask  E 
serves  as  a  condenser,  and  is  supplied  with  an  inlet-tube  reaching 


FIG.  13.* 

almost  to  the  surface  of  a  small  amount  of  water  in  the  bottom 
of  the  flask,  a  safety-tube  F  reaching  just  below  the  surface  of 
the  water,  and  an  exit-tube  connected  with  the  first  of  the 
wide-mouthed  bottles  H.  In  each  of  the  bottles  H  is  poured 
from  20  cc.  to  30  cc.  of  the  absorbent  solution,  and  sufficient 
water  to  fill  them  more  than  half  full. 

Into  the  previously  dried  flask  D  are  introduced  10  gms.  of 
the   drillings,  free   from   lumps.     The   apparatus   is  now  con- 

*  From  Blair's  Chemical  Analysis  of  Iron  and  Steel. 


96  A   MANUAL    OF  PRACTICAL   ASSAYING. 

nected  up,  and  a  slow  stream  of  hydrogen  run  through  it  until 
all  the  air  is  expelled,  when  the  glass  stop-cock  5  is  closed  and 
the  supply  of  hydrogen  is  shut  off  by  closing  the  glass  stop- 
cock L.  If  the  connections  are  all  right  the  water  in  the 
safety-tube  F  will  keep  its  level.  When  this  is  assured,  dis- 
connect the  tube  C  and  fill  the  bulb  with  50  cc.  of  strong 
hydrochloric  acid  and  50  cc.  of  water.  Replace  the  tube  C, 
turn  on  the  hydrogen,  and  open  the  stop-cock  5  so  as  to  allow 
the  acid  to  flow  into  the  flask  D,  drop  by  drop.  'When  the 
acid  has  all  run  into  D  regulate  the  supply  of  hydrogen  so  that 
the  gas  will  continue  to  pass  through  the  solutions  in  the 
bottles  H  at  the  rate  of  6  to  8  bubbles  a  second,  and  heat  the 
contents  of  the  flask  D  cautiously.  Finally,  heat  the  solution 
in  the  flask  D  to  boiling,  and  boil  for  a  few  minutes.  When 
the  metal  in  the  flask  is  completely  dissolved,  remove  the 
source  of  heat  and  continue  the  current  of  hydrogen  for  about 
ten  minutes,  regulating  its  flow  by  means  of  the  stop-cock  Z, 
to  prevent  any  reflux  of  the  liquid  in  H,  which  might  be  caused 
by  the  cooling  of  D.  Shut  off  the  hydrogen,  disconnect  the  ap- 
paratus, and  wash  the  contents  of  the  bottle  H  into  a  beaker. 

Many  methods  of  proceeding  with  the  analysis,  according 
to  the  absorbent  used,  have  been  proposed,  for  which  see  "  The 
Chemical  Analysis  of  Iron  and  Steel,"  by  Blair. 

Absorption  by  Ammoniacal  Solution  of  Cadmium  Sulph- 
ate.— T.  T.  Morrell  *  proposes  to  absorb  the  H2S  in  a  solution 
of  cadmium  sulphate  prepared  by  adding  ammonia  to  a  solution 
of  sulphate  of  cadmium  until  the  precipitate  formed  redissolves 
and  the  solution  is  clear.  This  solution  is  placed  in  the  bottles 
ff,  H,  and  the  analysis  conducted  as  described.  The  precipi- 
tated cadmium  sulphide  is  filtered  off,  and  washed  with  water 
containing  a  little  ammonia.  The  filter  containing  the  pre- 
cipitated cadmium  sulphide  is  now  placed  in  a  beaker  contain- 
ing a  little  cold  water,  and  sufficient  hydrochloric  acid  to 
dissolve  the  precipitate  is  added.  The  sulphur  may  now  be 
determined  by  titration  with  standard  iodine  solution. 

*  Chemical  News,  Vol.  XXVIII,  p.  229. 


SULPHUR. 


97 


The  method  of  determining  the  sulphur  by  standard  iodine 
solution  was  first  suggested  by  Elliott  *  and  requires  the  fol- 
lowing solutions : 

Iodine  Solution. — Dissolve  6.5  gms.  of  pure  iodine  in  water 
with  9  gms.  of  potassium  iodide,  and  dilute  to  1000  cc. 

Hyposulphite  of  Sodium  Solution. — Dissolve-  25  gms.  of 
sodium  hyposulphite  in  water,  add  2  gms.  of  ammonium  car- 
bonate, and  dilute  to  1000  cc.  The  addition  of  ammonium 
carbonate  retards  the  decomposition  of  the  sodium  hyposul- 
phite. 

Starch  Solution. — Place  I  gm.  of  pure  wheat  starch  in  a 
porcelain  mortar  and  rub  into  a  thin  cream  with  water.  Pour 
into  150  cc.  of  boiling  water,  allow  to  stand  until  cold,  and 
decant  the  clear  solution.  A  fresh  solution  should  be  prepared 
every  few  days. 

Bichromate  of  Potassium  Solution. — Dissolve  5  gms.  of  pure 
potassium  bichromate  in  water  and  dilute  to  1000  cc. 

The  bichromate  solution  is  standardized  as  described  in  the 
determination  of  iron  (Part  II,  Chapter  XVI).  When  a  solu- 
tion of  potassium  bichromate  is  added  to  a  solution  of  potas- 
sium iodide  containing  free  hydrochloric  acid,  iodine  is  liberated 
as  follows: 

K2Cr207  +  6KI  +  I4HC1  =  8KC1  +  Cr2Cl6  +  ;H2O  +  61. 

Or,  I  equivalent  of  K2Cr2O7  (=  294.5)  liberates  6  equivalents 
(=  761.1)  of  iodine.  When  a  solution  of  hyposulphite  of 
sodium  is  added  to  a  solution  containing  free  iodine  the  follow- 
ing reaction  takes  place : 

2NaHS2O3  +  2!  =  2HI  +  Na2S4O6- 

By  adding  a  few  drops  of  starch  solution  to  a  solution  con- 
taining iodine,  blue  iodide  of  starch  is  formed,  and  colors  the 
solution  as  long  as  it  contains  free  iodine.  When  sufficient 
hyposulphite  is  added  to  such  a  solution  to  exactly  combine 
with  the  iodine,  the  blue  color  disappears.  Conversely,  upon 

"^Chemical  News,  Vol.  XXIII,  p.  61. 


9  A    MANUAL    OF  PRACTICAL   ASSAYING. 

the  addition  of  a  solution  of  iodine  to  a  solution  containing 
hyposulphite  of  sodium  and  a  little  starch,  the  blue  color  of 
the  iodide  of  starch  will  disappear  as  fast  as  formed  until  all 
the  triosulphate  has  been  converted  into  tetrathionate,  and 
then  the  slightest  excess  of  iodine  will  give  the  solution  a  per- 
manent blue  color.  The  same  is  true  of  a  solution  containing 
free  H2S,  the  reaction  being  H2S  +  2!  =  2HI  +  S.  To  stand- 
ardize the  hyposulphite  solution  proceed  as  follows :  Dissolve 
I  gm.  of  pure  potassium  iodide  in  300  cc.  of  water,  add  5  cc 
of  hydrochloric  acid,  and  then  25  c.c.  of  the  standardized  bi- 
chromate solution,  which  will  liberate  a  known  amount  of 
iodine.  Now  add  from  a  burette  the  hyposulphite  solution 
until  the  blue  color  nearly  disappears,  add  a  few  drops  of  starch 
solution,  and  continue  the  addition  of  the  hyposulphite  solu- 
tion until  the  blue  color  disappears  entirely.  The  amount  of 
iodine  being  known,  the  value  of  the  hyposulphite  solution  is 
readily  calculated  from  the  reading  of  the  burette.  Now 
measure  off  into  a  beaker  25  cc.  of  the  hyposulphite  solution, 
dilute  to  300  cc.,  add  a  few  drops  of  starch  solution,  and  run 
in,  from  a  burette,  standard  iodine  solution  until  the  blue  color 
is  permanent.  The  value  of  the  hyposulphite  solution  being 
known,  that  of  the  iodine  solution  can  be  readily  calculated. 
(See  Part  IV,  Chapter  II.) 

Having  prepared  and  standardized  the  solutions  the  actual 
determination  is  performed  by  titrating  the  solution  containing 
the  sulphur  with  the  standard  iodine  solution  in  the  manner 
just  described. 

Absorption  by  Alkaline  Solution  of  Lead  Nitrate. 
— To  prepare  the  solution  pour  a  cold  solution  of  nitrate  of 
lead  into  a  solution  of  potassium  hydrate  (1.27  sp.  gr.),  stirring 
constantly  to  dissolve  the  oxide  of  lead,  which  precipitates. 
Continue  the  addition  of  lead  nitrate  until  a  permanent  pre- 
cipitate is  formed.  Allow  the  precipitate  to  settle,  and  siphon 
the  clear  liquid  into  a  glass-stoppered  bottle.  To  prevent  the 
stopper  sticking,  coat  it  with  a  little  paraffine. 

From  20  to  30  cc.  of  this  solution  is  poured  into  the  bottles 
H,  H,  and  water  added  until  the  bottles  are  more  than  half 


SULPHUR.  99 

full.  The  decomposition  and  absorption  are  conducted  as 
previously  described.  When  the  operation  is  completed  rinse 
out  the  bottle  //'.(should  the  second  bottle  contain  a  precipitate 
this  must  be  added  to  the  contents  of  the  first)  into  a  beaker 
and  filter,  washing  with  hot  water  until  the  washings  no  longer 
give  a  reaction  for  lead  when  treated  with  a  drop  of  acetic  acid 
and  potassium-chromate  solution.  Transfer  the  lead  sulphide 
to  a  beaker,  and  dissolve  in  a  little  dilute  nitric  acid,  being  care- 
ful to  use  as  little  acid  as  possible.  Add  a  slight  excess  of  sul- 
phuric acid  and  boil.  Dilute  with  hot  water,  add  a  slight 
excess  of  ammonia,  and  then  a  slight  excess  of  strong  acetic 
acid.  The  lead  sulphate  will  be  dissolved,  when  the  solution  is 
ready  for  titration  with  standard  solution  of  ammonium  molyb- 
date,  after  dilution  to  about  180  cc.  with' hot  water.  The  lead 
is  precipitated  as  a  molybdate,  and  the  end  reaction  obtained 
by  means  of  a  solution  of  tannin,  in  the  manner  described  in 
the  volumetric  determinations  of  sulphur  and  lead.  Having 
the  standard  of  the  molybdate  solution  in  terms  of  lead,  its- 
standard  for  sulphur  may  be  obtained  by  the  factor  0.1548. 

Generally  the  carbonaceous  residue  left  after  treating  pig- 
iron  with  hydrochloric  acid  will  contain  sufficient  sulphur  to 
seriously  affect  the  results  of  the  analysis.  Hence  where  an 
accurate  determination  of  sulphur  in  pig-iron  is  required  the 
examination  of  the  carbonaceous  residue  should  never  be 
neglected  when  the  evolution  method  is  employed.  To  deter- 
mine the  sulphur  in  this  residue  transfer  the  contents  of  flask 
D  to  a  beaker  and  filter,  using  the  filter-pump  and  platinum 
cone  and  a  strong  filter-paper;  wash  thoroughly,  first  with  a 
little  dilute  hydrochloric  acid,  and  finally  with  water.  Dry  the 
residue  on  the  filter,  and  determine  the  sulphur  by  some  of  the 
methods  previously  described,  preferably  by  fusion. 


CHAPTER  III. 


PHOSPHORUS  (P). 

A  number  of  different  methods  have  been  proposed  for 
the  determination  of  phosphorus  in  iron  ores,  pig-iron,  steel, 
etc.,  but  the  volumetric  method,  as  described  below,  and  the 
standard  gravimetric  method  are  the  only  ones  in  general  use 
at  present  in  the  United  States. 

Volumetric  Method. — This  method,  as  originally  described 
by  Mr.  B.  B.  Wright,*  and  improved  by  Mr.  F.  A.  Emmerton,f 
is  applicable  for  phosphorus  determinations  in  ores,  steel,  etc., 
and  the  writer  believes  is  as  rapid  and  accurate,  provided  the 
necessary  precautions  are  observed,  as  any  method  which  we 
have.  It  is  rapidly  being  adopted  by  our  iron  and  steel  chem- 
ists as  a  standard  method. 

Steels,  Pig  and  Wrought  Iron. — Dissolve  5  grammes  of  drill- 
ings in  a  dish  (about  6  inches  in  diameter)  in  75  cc.  of  nitric 
acid  of  1. 20  sp.  gr.,  cover  the  dish  with  a  watch-glass,  placed 
on  a  glass  triangle  so  that  there  is  a  space  between  the  rim  of 
the  dish  and  the  watch-glass,  and  boil  down  to  dryness  on  the 
sand-bath  or  hot  iron  plate.  Heat  on  the  plate  or  bath  for 
about  30  minutes  after  the  mass  has  gone  to  dryness,  at  the 
end  of  which  time  all  the  free  acid  should  have  been  expelled. 
Remove  from  the  source  of  heat,  cool,  and  add  40  cc.  of  con- 
centrated hydrochloric  acid,  and  place  the  watch-glass  on  the 
casserole.  Heat  gently  until  the  iron  goes  into  solution,  and 
then  boil  down  until  all  but  about  15  cc.  of  the  acid  is  driven 
off.  The  boiling  down  of  the  solution  requires  attention,  as  it 

*  Transactions  of  American  Institute  of  Mining  Engineers,  Vol.  X,  page  197. 
\  Ibid.,  Vol.  XV,  page  93. 

100 


PHOSPHORUS.  101 

is  necessary  that  the  solution  should  be  very  concentrated,  and 
at  the  same  time  there  should  be  very  little  ferric  chloride 
dried  on  the  sides  of  the  casserole,  as  this  will  be  difficult  to 
redissolve.  Let  the  casserole  cool,  wash  off  the  watch-glass 
with  40  cc.  of  concentrated  nitric  acid,  allowing  the  acid  to 
run  down  into  the  casserole.  Cover  the  casserole  with  a  glass 
funnel,  and  boil  down  to  about  15  cc.  in  bulk.  Remove  the 
casserole  from  the  source  of  heat,  and  move  its  contents  so  as 
to  moisten  whatever  crust  may  have  formed  on  the  sides. 
The  solution  is  now  practically  free  from  hydrochloric  acid, 
and  should  be  diluted  with  water  and  washed  into  a  4<DO-cc. 
flask,  bringing  the  bulk  of  it  to  about  75  cc.  Add  strong  am- 
monia, shaking  thoroughly  after  each  addition.  Continue  to 
add  ammonia  until  the  mass  sets  to  a  stiff  jelly,  and  add  a 
few  cc.  more.  There  should  be  a  strong  smell  of  ammonia  in 
excess  after  shaking.  Then  add  concentrated  nitric  acid,  shak- 
ing well  after  each  addition,  until  the  solution  begins  to  get 
thinner.  After  the  precipitate  has  all  dissolved,  and  the  solu- 
tion shows  a  very  dark  color,  add  sufficient  nitric  acid  to  bring 
the  solution  to  a  clear  amber  color.  The  solution  should  now 
have  a  bulk  of  about  250  cc.  Immerse  a  thermometer  into  the 
solution,  and  heat  or  cool  carefully  until  it  has  a  temperature 
of  85°  C.  When  the  solution  has  a  temperature  of  85°  C.  add 
40  cc.  of  ammonium-molybdate  solution  (prepared  by  dissolving 
100  grammes  of  molybdic  acid  in  a  mixture  of  300  cc.  of  strong 
ammonia  and  100  cc.  of  water,  and  pouring  this  solution  into 
1250  cc.  of  nitric  acid  of  1.20  sp.  gr.).  Close  the  flask  with  a 
stopper,  wrap  it  in  a  thick-warm  cloth,  and  shake  violently  for  5 
minutes.  This  covering  with  a  cloth  is  necessary,  as  the  temper- 
ature of  the  solution  must  not  vary  much  from  85°  C.  Collect 
the  yellow  precipitate  on  a  filter,  using  the  filter-pump  to  filter 
rapidly,  and  wash  the  flask  and  precipitate  with  a  solution  of 
ammonium  sulphate  [(NH4)2SO4  crystals,  25  grammes;  H2SO4 
cone.,  50  cc. ;  H2O,  2500  cc.].  Dissolve  the  washed  precipitate 
in  ammonia.  If  a  small  portion  of  the  precipitate  should 
adhere  to  the  sides  of  the  flask  it  may  be  dissolved  with  a 
portion  of  the  ammonia  used  to  dissolve  the  yellow  precipitate 


102  A    MANUAL    OF  PRACTICAL   ASSAYING. 

on  the  filter.  Place  about  10  grammes  of  granulated  zinc 
(the  same  as  is  used  in  the  determination  of  iron ;  see  Chap- 
ter XVI)  in  a  5OO-cc.  flask,  place  the  funnel  containing  the 
yellow  precipitate  in  the  neck  of  the  flask,  and  wash  the 
precipitate  into  the  flask  with  dilute  ammonia  (i  in  4),  using 
about  30  cc.  A  larger  amount  of  ammonia  than  is  absolutely 
necessary  is  to  be  avoided.  After  having  washed  with  ammo- 
nia wash  twice  with  water,  and  suck  dry  by  means  of  the 
filter-pump.  Pour  the  ammonia  solution  into  a  small  beaker, 
reinsert  the  funnel  in  the  flask,  and  pour  the  solution  in  the 
beaker  through  the  filter  again,  washing  the  paper  thoroughly 
with  water  after  the  ammonia  solution  has  all  run  through, 
finally  sucking  the  filter  dry  with  the  pump.  Pour  into  the 
flask  about  80  cc.  of  warm  dilute  sulphuric  acid  (i  in  4),  and 
heat  quickly  until  rapid  solution  of  the  zinc  commences,  and 
then  gently  stir  for  10  to  15  minutes,  at  the  end  of  which  time 
the  reduction  of  the  molybdic  acid  is  complete.  Filter  the 
liquid  from  the  undissolved  zinc  through  a  large  fluted  filter, 
rinse  the  flask  with  cold  water,  pouring  on  to  the  filter.  After 
these  washings  have  run  through,  rinse  the  flask  once  more 
with  cold  water,  pouring  on  to  the  filter  again.  The  filtration 
should  be  rapid,  so  as  to  expose  the  solution  to  the  air  as 
short  a  time  as  possible. 

The  filtrate  is  now  ready  for  titration  with  a  standard  solu- 
tion of  potassium  permanganate.  The  permanganate  solution 
is  run  in  until  the  solution  is  colorless,  it  having  been  of  a  dark 
olive-green  color  before  oxidation.  One  drop  of  permanganate 
solution  should  now  produce  a  pink  tint  when  the  titration  is 
stopped  and  the  reading  of  the  burette  taken.  A  convenient 
strength  to  have  the  permanganate  solution  is  i  cc.  =  o.oooi 
gramme  of  phosphorus.  Such  a  solution  may  be  made  by 
diluting  the  solution  used  for  iron  (Chapter  III)  with  distilled 
water  until  i  cc.  =  0.006141  gramme  iron.  As  0.9076  time 
this  value  gives  its  strength  in  terms  of  molybdic  acid  = 
0.005574,  and  1.794  per  cent  of  this  is  its  value  in  phosphorus 

=  O.OOOI. 


PHO  SPHOR  US.  103 

In  order  to  insure  good  results  with  this  method  the  above 
conditions  as  to  temperature,  etc.,  must  be  carried  out. 

Dr.  Drown*  has  proposed  a  method  of  effecting  the  solution 
of  a  pig-iron  or  steel  which  greatly  lessens  the  time  required. 
His  method  is  as  follows:  Dissolve  the  weighed  drillings  in 
nitric  acid  of  1.135  SP-  gr->  an^  allow  to  boil  one  minute;  then 
add  potassium-permanganate  solution  until  a  precipitate  of 
MnO2  appears.  Now  add  a  few  crystals  of  ferrous  sulphate 
(should  be  tested  for  phosphorus,  as  the  usual  c.  p.  salt  contains 
more  or  less.  The  phosphorus  free  salt  can  be  purchased  of 
Baker  &  Adamson,  Easton,  Pa.)  to  dissolve  the  precipitated 
MnOu.  Filter  the  solution  into  the  flask,  and  add  sufficient 
ammonia.  When  the  solution  clears  up,  add  a  few  drops  of 
permanganate  solution  to  insure  complete  oxidation,  again 
dissolving  with  ferrous  sulphate  if  necessary.  Precipitate  with 
ammonium-molybdate  solution,  proceeding  as  above,  and  using 
the  same  precautions. 

A  modification  of  the  above  method  has  been  proposed  by 
Handy,  f  which  consists  in  the  determination  of  the  acidity 
of  the  molybdate  precipitate  in  place  of  reducing  the  molybdic 
acid  and  titrating  with  permanganate.  The  following  solutions 
are  required  : 

Standard  Sodium  Hydrate. — Dissolve  15.4  grammes  of 
NaOH  in  100  cc.  of  water,  stir  in  saturated  barium-hydrate 
solution  until  a  precipitate  of  barium  carbonate  is  no  longer 
formed.  Filter  immediately,  and  dilute  to  two  litres. 

Standard  Nitric  Acid. — Make  a  stock  solution  of  200  cc.  of 
acid  (sp.  gr.  1.42)  in  two  litres  of  water.  For  approximate 
standard  dilute  200  cc.  of  this  solution  to  two  litres. 

These  two  solutions  should  be  made  to  agree  cc.  for  cc., 
and  had  also  best  be  brought  to  a  strength  of  I  cc.,  equal  to 
0.0002  gramme  of  phosphorus. 

The  sodium-hydrate  solution  is  standardized  by  o.i  gramme 
of  pure  molybdate  precipitate  obtained  from  acidified  ammo- 


*  Transactions  of  American  Institute  of  Mining  Engineers,  Vol.  XVIII. 
f  Journal  of  Analytical  and  Applied  Chemistry,  Vol.  VI,  p.  204. 


IO4  A   MANUAL   OF  PRACTICAL   ASSAYING. 

nium  or  sodium  phosphate,  washed  with  one  per  cent  nitric 
acid,  and  thoroughly  dried  at  100°  C.  The  precipitate  contains 
1.63  per  cent  phosphorus. 

As  an  indicator,  0.5  gramme  of  phenolphthalein  in  200  cc. 
of  95  per  cent  alcohol  is  used.  Three  drops  of  this  solution 
are  taken  for  each  titration. 

The  method  is  as  follows :  Dissolve  2  grammes  of  steel  in  a 
12-ounce  Erlenmeyer  flask  in  75  cc.  of  nitric  acid  (sp.  gr.  1.13),. 
and  add  15  cc.  of  potassium-permanganate  solution  (5  grammes- 
in  1000  cc.)  to  the  boiling  solution.  Boil  until  the  pink  color 
disappears.  If  brown  MnO2  separates,  the  oxidation  is  com- 
plete. Some  irons  and  steels  will  require  more  permanganate,, 
especially  those  high  in  carbon.  Remove  momentarily  from 
the  heat,  add  about  -^  gramme  of  granulated  sugar,  and  heat 
until  the  solution  clears.  Allow  to  cool  for  a  few  minutes  and 
then  add  13  cc.  of  ammonia  (sp.  gr.  0.90),  pouring  carefully 
down  the  sides.  Agitate  until  the  ferric  hydrate  is  dissolved, 
and  cool  or  heat  to  85°  C.  Add  50  cc.  of  the  molybdate 
solution,  cork,  wrap  the  flask  in  a  towel,  and  shake  for  five 
minutes.  Filter  immediately,  wash  five  times  with  a  one  per 
cent  solution  of  nitric  acid,  and  then  five  times  with  a  one 
per  cent  solution  of  potassium  nitrate.  Place  the  filter  and  its 
contents  in  the  flask,  add  10  to  20  cc.  of  the  standard  sodium- 
hydrate  solution,  and  shake  a  few  times  to  dissolve  the  precipi- 
tate. Add  three  drops  of  the  indicator  solution  and  titrate 
back  with  the  standard  nitric-acid  solution.  The  titration 
must  be  performed  quickly,  and  as  soon  as  the  precipitate 
is  completely  dissolved. 

Iron  Ores. — Dissolve  from  2  to  10  grammes  of  ore  in  hydro- 
chloric acid  (sp.gr.  1.12),  and  proceed  as  above.  The  insoluble 
residue  can  be  filtered  off  and  fused  with  sodium  carbonate 
(see  Part  II,  Chapter  I)  if  necessary,  the  fused  mass  being 
dissolved  in  dilute  sulphuric  acid,  and  the  solution  added  to- 
the  nitric-acid  solution. 

Coal  and  Coke. — The  phosphorus  will  be  found  in  the  ash. 
Weigh  out  IO  grammes  of  the  coal  or  coke,  and  ignite  it  over 
the  blast-lamp  or  in  the  muffle-furnace  until  nothing  but  ash 


PHOSPHORUS.  IO5 

remains.  Fuse  the  ash  with  sodium  carbonate,  and  proceed  as 
above. 

In  the  case  of  ores  or  pig-iron  containing  arsenic  the  arsenic 
will  be  precipitated,  together  with  the  phosphorus,  upon  the 
addition  of  the  molydate  solution,  as  above.  In  this  case  if 
the  temperature  of  the  solution  is  not  above  25°  C.,*  when  the 
molybdate  solution  is  added  the  arsenic  will  remain  in  solution, 
whilst  the  phosphorus  will  be  completely  precipitated.  As  the 
steel  metallurgists  consider  arsenic  quite  as  detrimental  to  the 
quality  of  the  pig  as  phosphorus  this  precaution  is  not  usually 
taken. 

Gravimetric  Method. — Proceed  as  above  until  the  yellow 
precipitate  is  obtained,  filtered,  and  washed,  such  care  in  regard 
to  the  temperature  of  the  solution  before  adding  the  molyb- 
date 'solution  being  unnecessary  in  this  case.  Dissolve  the 
yellow  precipitate  with  ammonia  as  before,  filtering  into  a 
beaker  ;  make  the  solution  acid  with  dilute  hydrochloric  acid 
and  then  alkaline  with  ammonia  in  excess  ;  cool,  and  when  cold 
add  5  cc.  of  magnesia  mixture.  Allow  to  stand  in  a  cool  place 
for  several  hours  with  frequent  agitation  (see  Part  II,  Chapter 
XXIV);  finally  filter,  wash,  ignite,  and  weigh  as  in  the  case  of 
the  determination  of  magnesia. 

The  weight  of  the  magnesia  pyrophosphate  obtained,  mul- 
tiplied by  0.27928,  equals  the  weight  of  phosphorus  in  the 
amount  of  substance  taken. 

For  comparative  results  and  much  valuable  information 
regarding  the  determination  of  phosphorus  in  steel,  see  Trans, 
of  the  American  Institute  of  Mining  Engineers,  meeting  of 
October,  1895,  Vol.  XXV. 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  Feb.,  1893. 


CHAPTER  IV. 

CARBON  (C). 

FOR  the  determination  of  carbon  in  organic  substances  the 
reader  is  referred  to  works  that  treat  of  such  determinations. 

The  determinations  of  carbon  in  steel,  pig-iron,  etc.,  are 
about  the  only  determinations  of  carbon  which  the  metallur- 
gical chemist  will  be  called  upon  to  make,  except  the  determi- 
nation of  carbon  in  fuels,  for  which  the  reader  is  referred  to 
Part  III,  Chapter  X. 

The  carbon  in  steel,  pig-iron,  etc.,  usually  exists  in  two 
conditions ;  that  is,  combined  (as  a  carbide)  and  uncombined 
(graphite).  Usually  the  combined  carbon  is  all  that  is  required. 
When  the  percentage  of  carbon  in  both  conditions  is  required, 
the  total  carbon  is  determined  in  one  portion  and  the  com- 
bined carbon  in  another.  The  difference  between  the  total 
amount  of  carbon  and  the  combined  carbon  gives  the  graphite. 
Or  the  graphite  may  be  determined,  the  difference  between 
the  amount  of  graphite  found  and  the  total  carbon  being  the 
combined  carbon. 

Many  methods  for  these  determinations  have  been  pro- 
posed, but  only  those  that  are  known  to  be  good  and  are  in 
general  use  will  be  given. 

Total  Carbon. — The  following  method,  which  was  first 
proposed  by  Arthur  Elliot,*  is  a  modification  of  Rodger's  and 
Ullgren's  methods.  It  is  believed  to  be  among  the  best  in 
use.f  Add  to  2  or  3  grammes  of  borings  or  filings  in  a  small 
beaker  50  cc.  of  a  solution  of  neutral  copper  sulphate,  prepared 

*  Chemical  News,  May,  1869. 

f  American  Chemist,  October,  1871.     Also  Cairns,  page  105. 

106 


CARBON.  ID/ 

by  dissolving  the  recrystallized  copper  sulphate  (as  sold  by 
dealers)  in  water,  adding  a  small  quantity  of  copper  oxide,  boil- 
ing until  the  copper  sulphate  begins  to  crystallize,  filtering  out 
the  excess  of  oxide,  and  concentrating  the  solution  until  it  is 
completely  crystallized.  Dry  the  crystals  by  draining  off  the 
water,  and  pressing  them  between  layers  of  bibulous  paper,  and 
dissolve  them  in  water  in  the  proportion  of  I  part  of  salt  to  5 
parts  of  water. 

After  heating  the  solution  of  copper  sulphate  containing 
the  iron  about  TO  minutes,  by  which  means  the  iron  is  dissolved 
and  the  copper  precipitated,  add  20  cc.  of  a  solution  of  cupric 
chloride  (containing  one  part  of  salt  in  two  parts  of  water)  and 
50  cc.  of  concentrated  hydrochloric  acid,  and  heat  to  a  point 
just  below  boiling,  with  frequent  stirring  until  the  precipitated 
copper  is  dissolved,  leaving  the  carbon  free.  Filter  out  the 
carbon  through  a  funnel  made  of  glass  tubing  about  five  eighths 
of  an  inch  in  diameter,  and  drawn  to  a  point  at  one  end.  Fill 
the  point  of  the  funnel  up  to  the  shoulder  with  broken  glass, 
and  place  upon  this  a  thin  layer  of  ignited  asbestos,  pressing  it 
gently  against  the  walls  of  the  funnel.  Care  should  be  taken 
not  to  make  the  layer  of  asbestos  too  thick  or  compact,  as  it  is 
liable  to  become  clogged  by  the  carbon  and  render  the  filtra- 
tion very  tedious.  Filter  off  into  a  clean  beaker,  and  should 
any  carbon  run  through,  as  it  is  liable  to  at  first  if  the  asbestos 
layer  is  too  thin,  pour  back  the  first  filtrate  into  the  filter. 
Transfer  all  of  the  carbon  to  the  filter,  and  wash  with  hot  water 
until  the  washings  no  longer  give  a  precipitate  with  silver  ni- 
trate. After  washing  all  of  the  carbon  down  from  the  sides  of 
the  tube,  cut  it  off  about  an  inch  above  the  layer  of  carbon,  by 
scratching  the  glass  with  a  file,  and  pressing  a  red-hot  glass 
against  the  cut.  Then  invert  the  part  containing  the  carbon 
into  the  mouth  of  the  decomposing  flask  of  an  apparatus  sim- 
ilar to  that  described  for  determining  carbonic  acid  *  (see  Part 
II,  Chapter  V),  and  blow  the  contents  into  the  flask,  avoiding 
the  use  of  water  by  wiping  out  any  carbon  that  may  adhere  to 

*  See  Cairns'  Quantitative  Analysis,  page  35. 


108  A    MANUAL    OF  PRACTICAL  ASSAYING. 

the  glass  with  a  little  piece  of  ignited  asbestos,  and  throwing 
this  also  into  the  flask.  To  the  filtrate  from  the  carbon  add  4 
or  5  cc.  of  concentrated  hydrochloric  acid  to  prevent  the  for- 
mation of  any  precipitate  of  basic  copper  salt,  and  dilute  with 
water  until  the  fluid  is  transparent.  If  any  carbon  should  have 
passed  through  the  asbestos  it  can  readily  be  seen  in  the  trans- 
parent fluid.  Should  there  be  any  filter  it  out  through  another 
filter  of  ignited  asbestos  and  transfer  it  also  to  the  flask.  Con- 
nect the  apparatus,  and  start  the  aspirator  very  slowly.  After 
the  aspirator  has  been  working  about  12  minutes,  disconnect 
the  absorption-tube  and  weigh  it.  Then  connect  again  and 
start  the  aspirator  very  slowly  again.  After  the  aspirator  has 
run  a  few  minutes  in  order  to  partially  exhaust  the  air  in  the 
apparatus,  introduce  through  the  funnel-tube  about  40  cc.  of 
the  chromic-acid  solution. 

This  solution  is  prepared  by  dissolving  3  gms,  of  chromic 
acid  in  a'little  water  and  adding  30  cc.  of  pure  concentrated 
sulphuric  acid.  This  should  be  heated  to  incipient  boiling 
and  then  cooled.  When  cold  it  is  ready  for  use. 

After  adding  this  solution  close  the  stop-cock  of  the  funnel- 
tube  and  heat  slowly  up  to  boiling.  After  the  acid  boils  re- 
move the  heat,  put  on  the  guard-tube,  open  the  stop-cock  of 
the  funnel-tube,  and  aspirate  slowly  until  the  absorption-tube 
is  cool.  After  it  is  thoroughly  cooled  weigh  it,  and  from  the 
increase  in  weight  due  to  the  carbonic  acid  (CO3)  calculate  as 
follows  :  The  weight  of  the  carbonic  acid  multiplied  by  0.27273 
equals  the  weight  of  carbon. 

In  place  of  the  copper  sulphate  and  copper  chloride,  the 
double  chloride  of  copper  and  ammonium  may  be  used.  The 
same  precautions  should  be  observed  as  in  the  determination 
of  carbonic  acid  by  direct  weight.  Some  chemists  prefer  to 
burn  the  carbon  obtained  in  the  above  manner  in  a  current  of 
oxygen  in  a  piece  of  combustion-tubing,  absorbing  the  resulting 
carbonic  acid  in  an  absorption-tube  similar  to  the  one  used 
above,  or  in  a  potash  bulb.*  (See  Part  III,  Chapter  X.) 

*  American  Chemist,  Vol.  VI,  September,  1875. 


CARBON.  ICQ 

Graphite. — The  best  and  safest  method  is  that  described 
by  Cairns  *  as  follows :  Dissolve  from  2  to  3  grammes  of  gray 
pig-iron  or  from  4  to  5  grammes  of  white  iron,  steel,  etc.,  in 
dilute  hydrochloric  acid  and  boil  for  half  an  hour,  filter 
through  asbestos  as  described  for  total  carbon,  wash  with  hot 
water  until  all  acid  is  washed  out,  then  with  a  strong  solution 
of  potassium  hydrate,  which  will  remove  silica ;  afterwards  with 
hot  water  to  wash  out  any  potassium  carbonate,  of  which  the 
potassium  hydrate  is  apt  to  contain  some ;  then  with  alcohol 
{which  will  remove  hydrocarbons),  until  the  alcohol  runs 
through  the  funnel  colorless.  Again  wash  with  a  little  hot 
water,  then  with  ether,  until  it  runs  through  colorless,  in  order 
to  displace  the  water  and  remove  another  class  of  hydrocarbons 
which  the  alcohol  may  have  failed  to  reach.  It  is  well,  finally, 
to  wash  with  a  little  hot  water  (particularly  if  the  ether  used  is 
not  perfectly  pure),  in  order  to  keep  the  graphite  from  adher- 
ing to  the  walls  of  the  funnel,  when  blown  into  the  decompos- 
ing flask,  being  careful  to  remove  any  excess  of  water  by 
gently  blowing  through  the  funnel.  After  the  graphite  is 
thoroughly  washed  it  is  transferred  to  the  decomposing  flask, 
and  oxidized  with  chromic  and  sulphuric  acids,  in  precisely  the 
same  manner  as  in  the  determination  of  total  carbon. 

The  objection  to  this  method  is  the  time  required  to  filter 
and  wash,  the  washings  with  potassium  hydrate  being  ex- 
tremely tedious. 

Eggerz's  modified  ^method  f  is  as  follows:  In  a  beaker  of 
100  cc.  capacity  mix  4  cc.  of  sulphuric  acid  and  20  cc.  of 
water,  and  when  the  heat  produced  by  the  combination  of  the 
water  and  the  acid  has  entirely  disappeared,  shake  2  grammes 
of  the  finely  powdered  pig-iron  into  the  dilute  acid,  and  boil 
for  half  an  hour.  (For  steel  and  wrought  iron  not  less  than  3 
grammes  should  be  taken,  and  the  acid  for  solution  should  be 
increased  in  proportion.)  The  solution  is  then  evaporated 
until  it  measures  18  cc.,  allowed  to  cool  to  the  temperature  of 
50°  C.,  and  4  cc.  of  nitric  acid  (of  1.20  sp.  gr.)  added ;  boil  for  a 

*  Cairns'  Quantitative  Analysis,  edition  1881,  page  114. 
f  Crook's  Select  Methods,  pages  79  and  So. 


1 10  A    MANUAL    OF  PRACTICAL   ASSAYING. 

quarter  of  an  hour,  and  allow  to  evaporate  on  a  water-bath 
until  on  holding  a  watch-glass  over  the  beaker  there  occurs  on 
it  no  perceptible  condensation.  To  the  dry  mass  add  30  cc.. 
of  water,  and  5  cc.  of  hydrochloric  acid  1.16  sp.  gr.;  boil  for  a 
quarter  of  an  hour,  and  add  more  hydrochloric  acid  if  there 
appears  to  be  anything  besides  silica  and  graphite  undissolved. 
The  insoluble  silica  and  graphite  are  thrown  on  a  filter  (which 
has  been  dried  at  100°  C.  and  carefully  weighed),  washed  with 
cold  water  until  the  washings  give  no  reaction  for  iron  when 
tested  with  potassium  ferrocyanide,  then  washed  with  boiling 
water  containing  5  per  cent  of  nitric  acid.  The  silica  and 
graphite  are  then  dried  on  the  filter  at  100°  C.  and  weighed, 
ignited  in  a  porcelain  crucible,  and  the  weight  carefully  taken. 
The  difference  between  the  weighings  before  and  after  ignition 
gives  the  amount  of  graphite. 

Combined  Carbon. — Dr.  Eggerz,  of  the  Swedish  School  of 
Mines,  first  proposed  a  method  of  determining  the  combined 
carbon  in  steel,  etc.,  by  comparing  the  color  of  a  solution  of 
the  iron  or  steel  under  examination  with  that  of  a  solution  of 
another  sample  of  which  the  carbon  percentage  was  known. 
This  method  is  based  upon  the  fact  that  when  steel  is  dissolved 
in  dilute  nitric  acid,  and  heated  until  the  separated  flocculent 
carbonaceous  matter  goes  into  solution,  the  liquid  assumes  a 
brown  color  proportionate  to  the  amount  of  combined  carbon 
present.  This  method  has  been  modified  from  time  to  time 
by  different  chemists  so  that  we  have  at  present  a  method 
which  is  not  only  rapid,  but  extremely  accurate  provided  the 
proper  precautions  are  observed.  A  number  of  standard 
solutions  for  comparison  have  been  proposed,  but  the  best 
and  safest  method  is  to  run  a  standard,  together  with  each  set 
of  determinations,  using  a  steel  or  iron  in  which  the  per- 
centage of  combined  carbon  has  previously  been  accurately 
determined.  This  standard  steel  should  be  as  nearly  like  the 
samples  to  be  treated  as  possible,  both  as  to  chemical  com- 
position and  mechanical  treatment.  Treat  the  standards  and 
samples  tp  be  teste4  exactly  alike  in  working,  the  same 


CARBON.  1 1  I 

amounts  being  taken.*  Drillings  are  preferable  to  filings,  as 
they  are  less  liable  to  contain  foreign  matter,  and,  being 
coarser,  dissolve  more  slowly.  Fine  particles  of  steel,  rich  in 
carbon,  dissolve  so  rapidly  that,  unless  special  precautions  are 
taken  to  keep  the  solution  cold,  some  of  the  carbon  is  oxid- 
ized and  given  off  as  a  gas.  From  o.i  to  0.2  gramme  are 
taken  for  analysis,  one  tenth  being  the  usual  amount  in  the 
case  of  steels. 

The  weighed  portions  are  best  dissolved  in  perfectly  dry 
(so  that  no  particles  will  stick  to  the  sides)  test-tubes  si* 
inches  long  and  about  five  eighths  of  an  inch  internal  diameter, 
the  sample  being  placed  in  the  test-tube,  which  is  then  im- 
mersed in  cold  water  and  the  dilute  nitric  acid  then  slowly  and 
steadily  poured  on.  A  very  convenient  form  of  apparatus  is  a 
beaker  or  other  vessel  about  7  inches  high,  which  is  half  filled 
with  cold  water  and  covered  with  a  perforated  tin  plate, 
through  the  holes  of  which  the  tubes  are  placed  and  thus 
steadied.  Nitric  acid  (free  from  organic  matter,  nitrous  fumes, 
and  chlorine)  of  about  1.20  sp.  gr.  is  used  to  effect  solution. 
The  ordinary  c.  p.  nitric  acid  is  1.40  sp.  gr.,  and  by  diluting 
this  one  half  with  distilled  water  an  acid  of  very  nearly  1.20  sp. 
gr.  is  obtained.  It  should  be  kept  in  a  dark  glass-stoppered 
bottle  and  in  a  dark  place.  The  following  amounts  of  dilute 
acid  for  one-tenth  gramme  of  steel  give  good  results  :  up  to 
0.20  per  cent  carbon,  2  cc.  of  acid  ;  from  0.20  up  to  0.50  per 
cent  carbon,  3  cc.;  from  0.50  per  cent  up  to  i.oo  per  cent 
carbon,  4  cc.;  i.oo  per  cent  up  to  1.75  per  cent,  6  cc.;  over  1.75 
per  cent  of  carbon,  8  cc.  The  most  convenient  method  of 
adding  the  acid  is  to  let  it  run  in  from  a  graduated  burette 
provided  with  a  glass  stop-cock. 

The  solution  must  not  be  heateot  until  all  action  has  ceased 
in  the  cold,  when  the  cold  water  in  which  the  tubes  are  im- 
mersed is  rapidly  brought  to  a  boil  and  boiled  for  15  minutes 
for  soft  steels  under  0.15  per  cent  carbon,  for  20  minutes  if 

*  Transactions  of  American  Institute  of  Mining  Engineers,  Vol.  XII,  page 
303- 


112  A    MANUAL    OF  PRACTICAL   ASSAYING. 

between  0.15  and  0.30  per  cent  carbon,  for  30  minutes  if  be- 
tween 0.30  and  0.80  per  cent  carbon,  and  45  minutes  if  above 
0.80   per   cent    carbon.     The    boiling   temperature    is   usually 
maintained,   although  for  special  reasons    other   temperatures 
are  often  used,  the  essential  point  being  to  always  maintain  the 
same  temperature  in  all  cases  where  fixed  standards  are  used, 
and  to  treat  the  standard  and  the  steel  under  examination  at 
exactly  the  same  temperature  where  standard  steels  are  used 
for  comparison,  as  is  recommended  here.    Sometimes  a  reddish- 
yellow  deposit  of  nitric  acid  and  ferric  oxide  forms  on  the  sides 
of  the  tubes  and  renders  the  solution  turbid  ;  in  such  cases  a 
low  temperature  of  about  70°  C.  is  preferable.     The  water-bath 
in  which  the  tubes  are  heated  may  be  provided  with  a  ther- 
mometer, and  the  evaporation  of  the  water  may  be  prevented 
by  the  addition  of  paraffine.     The  ceasing  of  the  evolution  of 
the  fine  bubbles  of  gas  from  the  clear  solution  is  an  indication 
of  the  completion  of  the  solution.     The  tubes  should  be  shaken 
from  time  to  time  during  the  heating,  and  the  iron  salt  should 
not  be  allowed   to  dry  on  the  walls  of  the   tubes.     The  color 
solutions  during  the  entire  operation  must  be  kept  out  of  the 
direct  rays  of  the  sunlight,  as  it  rapidly  fades  them.     The  color 
fades  more  rapidly  after  dilution  with  water  than  it  does  in  the 
strong  acid  solution.     After  heating,  the  tubes  may  be  cooled 
rapidly  by  plunging  into  cold  water.     If  the  percentage  of  car- 
bon is  high  (about   i.oo  per  cent)  the  solution   should  not  be 
allowed  to  stand  any  length  of  time  before  comparison  ;  if  the 
carbon  is  low  they  may  be  allowed  to  stand  at  least  two  hours. 
However,  it  is  best  to  cool  quickly.     After  the  solution  is  com- 
pleted it  must  be  diluted  with  at  least  its  bulk  of  water  to  get 
rid  of  the  tint  of  oxide  of  iron.     The  color  solution,  after  heat- 
ing, cooling,  and  diluting  with  distilled  water,  can  be  filtered 
from  the  graphite,  etc.,  through   an  ordinary  dry  filter-paper. 
The  quantity  of  water  added,  including  the  distilled  water  used 
for  cleaning  the  test-tube,  must  be  at  least  equal  to  the  quantity 
of  nitric  acid  used,  and  the  total  volume  must  never  be  less 
than  8  cc.  when  it  is  to  be  compared  with  the  standard  solution. 
The  solution  is  filtered  directly  into  a  burette  or  tube  for  com- 


CARBON.  113 

parison.  Tubes  of  about  one  half  an  inch  in  internal  diameter 
and  30  cc.  capacity  are  preferable,  and  it  is  generally  preferable 
to  calibrate  the  tubes  by  means  of  an  accurately  calibrated 
burette,  as  those  which  are  purchased  calibrated  often  show 
errors  of  considerable  importance.  The  tubes  used  for  the 
standard  and  the  different  determinations  should  be  of  exactly 
the  same  internal  and  external  diameters,  and  of  colorless  glass, 
and  provided  with  mouth -pieces  at  the  upper  ends.  The 
method  of  procedure  is  as  follows :  Suppose  the  standard  steel 
contains  0.75  per  cent  carbon  ;  if  we  dilute  the  solution  in  the 
tube  (thoroughly  mixing  after  each  addition  of  water)  to  15 
cc.,  then  each  cc.  will  contain  0.05  per  cent  of  carbon.  We 
now  dilute  the  solution  of  the  steel  in  which  the  carbon  is  to 
be  determined  with  distilled  water  until  its  color  exactly  cor- 
responds with  that  of  the  standard  steel,  and  then  take  the 
reading  of  the  height  of  the  liquid.  One  minute  should  be 
allowed  for  the  liquid  to  run  down  the  walls  of  the  tube  before 
taking  the  final  reading.  Suppose  it  reads  16  cc.;  then,  as  each 
cc.  contains  0.05  per  cent  carbon,  16  will  contain  0.80  per  cent. 
In  comparing  the  colors  it  is  usual  to  hold  a  piece  of  thin,  clear, 
white  paper  behind  the  tubes.  To  most  eyes  the  left-hand 
tube  will  appear  slightly  the  darkest.  A  good  plan  is  to  match 
the  colors  so  that  either  tube,  as  it  is  reversed,  will  appear 
darkest  when  it  is  placed  to  the  left.  This  appearance  can  be 
corrected  by  holding  the  tubes  a  little  to  the  right.  A.  E.  Hunt 
recommends  the  use  of  a  camera-shaped  box,  painted  black 
inside,  open  at  one  end  to  look  into,  and  having  a  frame  hinged 
at  the  bottom  which  is  covered  with  thin  white  paper  to  form 
a  background  for  the  tubes.  Near  this  end  have  an  opening 
in  the  frame  and  a  gutter  in  the  bottom  to  allow  the  tubes  to 
be  placed.  Hunt  says :  "  This  arrangement  I  have  found 
especially  useful  in  the  night-time,  when  I  used  a  fixed  Bunsen 
gas-burner  in  which  a  bead  of  carbonate  of  soda  on  a  platinum 
wire  gives  a  monochromate  flame.  It  is  placed  in  such  a  posi- 
tion as  to  have  the  rays  reflected,  by  means  of  the  hinged  frame 
of  paper  at  the  back,  upon  the  tubes.  I  have  been  enabled  in 
this  way  to  read  color  carbons  with  much  ease.  In  fact,  I  prefer 


114  A   MANUAL    OF  PRACTICAL   ASSAYING. 

this  means  of  comparison  to  daylight,  as  the  light  is  always 
under  control,  and  no  outside  rays  interfere  with  lights  and 
shadows."  It  is  preferable,  especially  where  color-carbon 
analyses  are  only  occasionally  made,  to  use  color  standards  of 
steel  with  each  set  of  analyses  in  the  manner  described.  Where 
many  samples  are  to  be  tested  every  day,  as  in  a  Bessemer- 
steel  works,  it  is  much  more  conveniently  and  rapidly  done  by 
simply  matching  the  diluted  test  with  a  rack  of  permanent 
standards  representing  different  percentages  of  carbon.  Per- 
manent standards  of  organic  substances,  as  burnt  sugar,  burnt 
coffee,  etc.,  are  not  satisfactory.*  Eggerz  describes  a  mixture 
of  chlorides  of  iron,  cobalt,  and  copper,  which  is  highly  recom- 
mended by  a  number  of  chemists  for  the  preparation  of  per- 
manent standards.  By  adding  to  the  neutral  chlorides  water 
containing  1.5  per  cent  hydrochloric  acid  for  the  chloride  of 
iron  and  0.5  per  cent  hydrochloric  acid  for  the  two  other 
chlorides,  solutions  can  be  prepared  of  a  strength  correspond- 
ing to  o.oi  gramme  of  metal  per  cubic  centimetre.  Then  8  cc. 
of  the  iron  solution  are  mixed  with  6  cc.  of  the  cobalt  solution 
and  3  cc.  of  the  copper  solution,  and  about  5  cc.  of  water  con- 
taining 0.5  per  cent  hydrochloric  acid  are  added  to  the  mixture. 
At  a  temperature  of  18°  C.  this  solution  shows  the  same  color 
as  a  solution  of  steel  in  dilute  nitric  acid  corresponding  to  o.i 
carbon  per  cubic  centimetre.  The  solution  may  be  afterwards 
diluted  with  water  containing  0.5  percent  hydrochloric  acid  to 
any  standard  color  required.  The  addition  of  water  is  almost 
directly  proportional  to  the  percentage  of  carbon.  The  standards 
thus  proposed  should  always  be  standardized  by  comparison 
with  solutions  of  steel  containing  a  known  amount  of  carbon. 
Frequently,  as  in  the  case  of  the  open -hearth  steel  process, 
only  a  few  minutes  can  be  allowed  for  the  determination  of 
the  carbon  in  tests  taken  from  the  furnace.  For  samples 
where  the  carbon  is  below  0.25  per  cent  a  quite  accurate  de- 
termination can  be  made  by  dissolving  o.io  gramme  of  the  fine 
drillings  in  2  cc.  of  1.20  nitric  acid  in  a  test-tube,  and  by  treat- 

*  Transactions  Institute  of  Mining  Engineers,  Vol.  X,  p.  186. 


CARBON.  115 

ing  the  standard  in  the  same  manner  and  at  the  same  time  in 
a  similar  tube  as  regards  diameter,  color,  and  thickness  of  glass, 
and  then  judging  of  the  variations  of  color  at  the  moment  of 
complete  solution  and  before  the  carbon  begins  to  separate 
out.  The  drillings  should  be  of  about  the  same  degree  of  fine- 
ness, so  that  they  will  dissolve  in  about  the  same  time.  When 
the  carbon  is  above  0.25  per  cent  the  drillings  are  dissolved  in 
4  cc.  of  dilute  nitric  acid,  which  has  previously  been  heated  in 
the  water-bath  to  a  point  below  boiling,  and  as  soon  as  the 
violent  ebullition  has  ceased,  boiled  by  holding  the  tubes  over 
a  burner  protected  by  a  piece  of  wire-gauze.  It  takes  about  4 
or  5  minutes'  boiling  to  effect  complete  solution,  and  a  few 
minutes  to  cool  sufficiently  in  cold  water.  When  the  solutions 
are  ready  to  decant  into  the  calibrated  tubes,  dilute  and  com- 
pare. The  color  solutions  prepared  in  this  way  are  much 
darker  than  when  prepared  in  the  usual  way  and  boiled  for 
several  minutes.  For  this  quick  work  a  number  of  weighed 
portions  of  standard  drilling  are  prepared  beforehand. 


CHAPTER  V. 

CARBONIC  ACID  (CO3), 

CARBON  dioxide  (usually  called  carbonic  acid)  may  be  deter- 
mined by  loss  of  weight  upon  heating,  provided  no  other  vola- 
tile matter  (such  as  water)  is  present,  loss  upon  treatment  with 
acids,  or  it  may  be  determined  by  direct  weight.  The  latter 
method  is  preferable,  and  is  more  satisfactory  in  all  cases. 

The  determination  by  direct  weight  consists  in  driving  off 
the  carbonic  acid,  by  means  of  heat  or  decomposition  of  the 
substance  by  acids,  conducting  it  over  into  a  weighed  absorp- 
tion apparatus.  The  increase  in  weight  of  the  absorption  ap- 
paratus represents  the  weight  of  the  carbonic  acid  driven  off. 
When  heat  is  used  as  the  decomposing  agent  the  apparatus 
described  for  the  determination  of  water  by  direct  weight 
(Chapter  VI)  may  be  employed.  The  apparatus  is  the  same 
as  before,  with  the  exception  that  between  the  calcium-chloride 
tube  and  the  last  U-tube  (the  one  connected  with  the  aspirator) 
is  connected  a  suitable  apparatus  for  the  absorption  of  the  car- 
bonic acid.  A  calcium-chloride  tube  filled  with  small  lumps 
of  freshly  prepared  soda  lime  is  a  very  good  form  of  absorption 
apparatus,  or  a  Liebig  potash  bulb  containing  a  strong  solution 
of  caustic  potash  may  be  used.  The  left-hand  end  of  the  com- 
bustion-tube should  also  be  connected  with  a  similar  absorption 
apparatus  in  order  that  all  air  which  enters  the  combustion-tube 
may  be  free  from  carbonic  acid.  The  substance  is  introduced 
into  the  combustion-tube  and  the  analysis  performed  in  the 
same  manner  as  described  for  water,  the  increase  in  weight  in 
the  absorption  apparatus  representing  the  carbonic  acid  (CO2) 
absorbed.  In  the  case  of  white-lead  and  similar  substances  the 
water  and  carbonic  acid  may  be  determined  in  this  way  by  one 

116 


CARBONIC  ACID. 


117 


operation.  When  acids  are  used  as  the  decomposing  agent  the 
form  of  apparatus  will  be  slightly  different.  In  place  of  the 
combustion-tube  a  decomposing  flask  is  used.  A  wide-necked 
glass  flask  of  about  300  cc.  capacity,  provided  with  a  tight  rub- 
ber stopper  with  three  perforations,  answers  the  purpose.  In 
one  of  the  holes  is  fitted  a  piece  of  bent-glass  tubing,  provided 
with  a  glass  stop-cock  or  a  piece  of  rubber  tubing  and  a  pinch- 
cock.  The  tube  should  enter  the  neck  of  the  flask  about  one 
inch.  This  will  be  designated  a.  A  funnel-tube  provided  with 
a  glass  stop-cock  should  enter  the  flask  through  the  second  hole. 
The  bottom  of  the  funnel-tube  should  reach  to  within  about 
an  inch  of  the  bottom  of  the  flask  so  that  its  end  will  be  covered 
by  the  fluid  in  the  flask.  This  will  be  designated  b.  Through 
the  third  hole  pass  a  piece  of  bent-glass  tubing  so  that  its  end 
is  flush  with  the  bottom  of  the  rubber  stopper.  To  a  attach 
a  chloride  of  calcium  tube  filled  with  soda-lime,  close  the  stop- 


FlG.   14. 


cock  of  b,  and  attach  to  c  a  series  of  three  U-tubes  partially 
filled  with  pumice  and  sulphuric  acid,  as  before.  To  the  last 
U-tube  of  the  series  attach  a  calcium-chloride  tube  filled  with 
soda-lime,  or  similar  absorption  apparatus,  and  to  the  right- 
hand  end  of  the  tube  attach  another  U-tube  filled  with  pumice 
and  soda-lime  to  prevent  moisture  finding  its  way  back.  To 
this  last  U-tube  attach  the  aspirator,  and  start  slowly  so  as  to 


Il8  A   MANUAL   OF  PRACTICAL  ASSAYING. 

pass  a  current  of  air  through  the  apparatus.  To  perform  the 
analysis,  disconnect  the  absorption-tube,  and  after  carefully 
weighing  reconnect  it.  Into  the  decomposing  flask  introduce 
about  25  cc.  of  water  and  then  a  weighed  amount  of  the  sub- 
stance. Replace  the  stopper  and  close  the  stop-cock  of  a  and 
b.  Start  the  aspirator  and  introduce  into  the  funnel  at  b 
some  strong  sulphuric  acid,  turning  the  stop-cock  of  b  gradually, 
so  as  to  allow  a  small  amount  of  acid  to  run  into  the  flask. 
The  aspirator  should  be  run  slowly  so  as  to  pass  a  slow  current 
through  the  apparatus,  and  the  acid  should  be  added  slowly 
by  means  of  the  stop-cock  b.  After  sufficient  acid  has  been 
added  and  all  ebullition  of  gas  has  practically  ceased,  gradually 
heat  the  contents  of  the  flask  by  means  of  the  flame  of  a  lamp 
or  burner.  Open  the  stop-cock  a  and  continue  to  run  the  aspi- 
rator until  the  volume  of  air  in  the  apparatus  has  been  changed 
four  or  five  times.  Disconnect  the  absorption-tube  and  weigh. 
The  increase  in  weight  represents  the  carbonic  acid  driven  off 
and  absorbed. 


CHAPTER  VL 
WATER  (HaO). 

WATER  may  exist  in  two  states  in  ores,  etc.,  uncombined 
(moisture)  and  combined  (water  of  crystallization). 

Moisture. — To  determine  the  moisture  in  an  ore,  heat  a 
weighed  amount  of  the  pulverized  sample  at  100°  to  105°  C.  in 
a  weighed  porcelain  crucible  to  constant  weight.  The  loss  in 
weight  represents  the  moisture  expelled  in  drying.  A  hot-air 
bath  provided  with  a  thermometer  is  the  most  convenient  ap- 
paratus in  which  to  perform  the  drying. 

In  the  case  of  coal,  coke,  etc.,  it  is  advisable  to  raise  the 
temperature  of  the  bath  to  about  115°  C. 

In  a  metallurgical  works  the  sample  will  usually  be  given  to 
the  chemist  with  the  moisture  expelled,  it  having  been  previ- 
ously dried  by  steam  at  the  sampling-works,  where  the  percent- 
age of  moisture  in  the  lot  or  shipment  of  ore  is  determined.  A 
good  method  to  be  pursued  at  a  sampling-works  is  as  follows : 
One  or  more  samples  of  a  little  over  a  pound  each  are  taken 
from  each  car  or  wagon  load  of  ore  as  it  comes  into  the  yard^  ca**e 
being  exercised  to  take  for  a  sample  the  fine  and  coarse  ore  in 
about  the  same  proportions  as  they  exist  in  the  car  or  wagon 
load,  and  to  take  the  sample  from  different  parts  of  the  load. 
The  lumps  of  ore  are  then  broken  up  and  one  pound  of  the 
sample  weighed  out  into  the  ordinary  assay-pan.  A  good  plan 
of  keeping  track  of  the  samples  is  to  write  the  number  of  the 
car  on  a  piece  of  wood  and  stick  it  in  the  sample.  A  conven- 
ient drier  can  be  made  of  boiler-iron.  It  should  be  several  feet 
in  length  and  at  least  3  feet  in  width,  if  many  determinations 
are  to  be  made  in  the  course  of  the  day  as  is  the  case  in  most 
smelting-works,  and  about  6  inches  in  depth.  The  joints 

119 


I2O  A    MANUAL    OF  PRACTICAL   ASSAYING. 

should  be  steam-tight.  The  exhaust-steam  from  the  engine  is 
conducted  into  the  box  and  heats  the  iron  plate  upon  which 
the  sample-pans  are  placed.  A  good  plan  is  to  take  the  samples 
in  the  afternoon,  and,  after  weighing  out,  let  them  dry  over 
night  on  the  dryer.  The  Fairbanks  Scales  Company  make  a 
very  convenient  scales  for  this  purpose.  The  top  of  the  beam 
is  graduated  into  ounces  and  the  bottom  into  percentages. 
When  the  weight  is  on  the  end  of  the  beam  the  scales  will 
weigh  one  pound.  After  drying,  transfer  the  sample  to  the 
pan  of  the  scales  and  weigh  ;  the  indicator  of  the  weight  will 
show  the  percentage  of  moisture  lost.  From  the  percentages 
thus  found  calculate  the  total  pounds  of  moisture  in  the  lot  of 
ore. 

Combined  Water. — The  method  to  be  pursued  will  depend 
on  the  character  of  the  substance.  When  the  substance  con- 
tains no  volatile  matter  which  is  driven  off  by  heating  except 
water,  and  does  not  undergo  oxidation  upon  heating,  heat  to 
redness  over  the  flame  of  a  burner  or  in  the  muffle-furnace  and 
weigh.  Heat  and  weigh  again,  and  repeat  the  operation  until 
the  crucible  and  contents  no  longer  lose  weight  by  being 
heated. 

When  volatile  matter  other  than  water  is  present,  as  for 
example  white-lead,  which  contains  both  water  and  carbonic 
acid,  a  direct  determination  of  the  water  is  necessary.  The 
following  method  will  serve  for  most  substances : 

Prepare  a  piece  of  combustion-tubing,  about  12  inches  in 
length,  and  to  the  left-hand  end  attach  a  suitable  drying  ap- 
paratus so  that  all  air  entering  the  tube  will  be  perfectly  dry. 
A  very  good  form  of  drying  apparatus  can  be  made  of  three  U- 
tubes  about  5  inches  in  length,  and  nearly  filled  with  small 
lumps  of  pumice.  Then  pour  into  each  tube  sufficient  con- 
centrated sulphuric  acid  to  fill  the  tubes  about  one  third,  pour- 
ing the  acid  over  the  pumice,  so  as  to  saturate  it.  The  U-tubes 
are  connected  together  and  to  the  combustion-tube  by  perfo- 
rated rubber  stoppers  and  pieces  of  glass  tubing.  All  joints 
can  be  made  perfectly  tight  with  paraffine.  To  the  right-hand 
end  of  the  combustion-tube  attach  a  calcium-chloride  tube 


WATER.  121 

filled  with  small  lumps  of  freshly  prepared  calcium  chloride. 
To  prepare  the  calcium  chloride,  break  it  into  small  lumps  and 
heat  to  redness  in  a  clay  crucible.  After  cooling  in  a  dry  place 
it  is  ready  for  use.  To  the  other  end  of  the  calcium-chloride 
tube  attach  a  U-tube  filled  with  pumice  and  sulphuric  acid,  as 
before,  to  prevent  any  moisture  finding  its  way  back.  When 
the  apparatus  is  all  connected  attach  the  last  U-tube  to  the 
aspirator  (the  filter-pump  makes  a  very  convenient  aspirator) 
and  start  a  slow  current  of  air  through  the  apparatus.  Gently 
warm  the  combustion-tube,  by  holding  the  flame  of  a  burner 
under  it,  to  expel  any  moisture  there  might  be  in  the  tube. 
After  the  current  of  air  has  passed  through  the  apparatus  tor 
about  15  minutes,  disconnect  the  calcium-chloride  tube  and 
weigh  it  carefully.  Now  introduce  one  or  more  grammes  of 
the  substance  into  the  combustion-tube  by  means  of  a  weighed 
platinum  or  porcelain  boat,  reconnect  the  calcium-chloride  tube, 
and  start  the  aspirator  slowly.  Heat  the  substance  in  the  boat 
by  means  of  a  good  burner,  gradually  bringing  to  redness,  and 
continue  to  heat  for  some  time,  finally  moving  the  flame  along 
the  combustion-tube  to  expel  any  moisture  that  may  have  con- 
densed on  its  sides.  Cool  and  whilst  cooling  continue  to  run 
the  aspirator.  Disconnect  the  calcium-chloride  tube  and  weigh 
it.  Its  increase  in  weight  will  be  due  to  the  moisture  absorbed 
by  the  calcium  chloride.  From  the  amount  of  substance  taken 
calculate  the  percentage  of  water. 


CHAPTER   VII. 

GOLD   (Au)   AND   SILVER    (Ag). 

As  gold  and  silver  are  generally  associated  together  in  ores, 
and  as  their  methods  of  assay  are  similar,  they  will  be  treated 
of  together  in  the  following  pages. 

Gold  is  universally  determined  and  weighed  as  metallic 
gold.  In  ores  it  is  universally  determined  by  fire-assay,  the 
assay  occasionally  being  preceded  by  treatment  of  the  ore  with 
acids  (Part  III,  Chap.  IV),  and  occasionally  being  preceded  by 
roasting  of  the  ore.  Silver  is  determined  in  the  same  manner, 
the  ore  or  furnace-product  sometimes  undergoing  treatment 
with  acids  or  roasting  previous  to  assay.  Alloys,  such  as  silver 
bullion,  are  treated  by  special  methods,  either  fire-assay  or 
volumetric  assay  in  the  wet  way  (Part  III,  Chapters  II  and 
III). 

The  fire-assay  is  general  in  its  application,  and  is  the 
method  universally  adopted  for  estimating  the  gold  and  silver 
contents  of  ores,  mattes,  slags,  etc.  The  results  are  not  abso- 
lutely accurate,  as  there  is  necessarily  a  loss  of  both  gold 
and  silver  in  fusion,  scorification,  and  cupellation.  The  most 
serious  loss  takes  place  in  cupellation,  the  precious  metals 
being  carried  into  the  cupel  and  off  in  the  fumes.  On  the 
other  hand,  the  gold  and  silver  buttons  may  be  contaminated 
with  certain  impurities  of  the  ores  under  treatment,  and  the 
silver  buttons  with  oxides  of  silver  and  lead,  and  the  final  gold 
beads  with  silver.  When  necessary,  corrections  may  be  made 
for  these  differences,  but  such  corrections  are  not  usual  in 
commercial  work,  except  in  the  assay  of  gold  bullion  and 
silver  bullion. 

The  fire-assay  consists  essentially  in  the  collection  of  the 

122 


GOLD   AND   SILVER.  123 

gold  and  silver  in  a  button  of  metallic  lead  either  by  scorifica- 
tion  (scorification  method)  or  by  fusion  (crucible  method). 
The  lead  button  is  then  freed  from  the  adhering  slag  by  ham- 
mering on  an  anvil,  and  is  finally  hammered  into  the  form  of 
a  cube  when  it  is  ready  for  cupellation. 

Both  the  scorification  and  crucible  methods  are  extensively 
used,  the  general  practice  in  Colorado  being  to  determine  the 
silver  in  two  or  more  portions  of  the  ore  by  scorification  and 
the  gold  in  two  or  more  portions  by  crucible  assay.  On  the 
Pacific  coast  the  crucible  method  is  the  favorite  one  for  both 
gold  and  silver.  Both  methods  have  their  advocates,  but  we 
believe  the  Colorado  practice  is  preferable,  as  most  ores  will 
yield  higher  silver  results  by  scorification  and  higher  and  more 
uniform  gold  results  by  crucible  assay.  The  reason  that  the 
crucible  method  gives  better  results  on  gold  is  owing  to  jts 
allowing  larger  quantities  to  be  taken  for  assay,  and  hence  a 
larger  button  of  gold  is  obtained  for  weighing  than  in  the 
scorification-assay,  where  only  a  small  quantity  can  be  taken, 
resulting  in  a  small  button,  which  introduces  a  source  of  error 
in  the  weighing  and  calculation  of  results.  This  can  be  obvi- 
ated by  running  a  number  of  scorifications  and  combining  the 
buttons  in  parting. 

Scorification-assay. — The  quantity  of  ore  taken  for  assay 
will  depend  upon  the  grade  and  character  of  the  ore  and  the 
size  of  the  scorifiers  on  hand.  The  amounts  usually  taken  are 
y1^  or  T?0  assay-tons.  The  table  on  the  next  page  gives  the 
charges  upon  the  basis  of  -^  A.  T.  ton. 

Litharge  added  to  the  assay  as  a  cover,  in  the  case  of 
pyrites  and  mattes,  helps  the  assay.  A  mixture  of  equal  parts 
of  sodium  bicarbonate  and  nitre  effects  the  same  results. 

Arsenical  and  copper  pyrites,  speiss,  and  copper  mattes 
containing  a  high  percentage  of  copper  are  preferably  assayed 
by  special  method. 

On  most  ores  a  charge  consisting  of  ore  T^  A.  T.,  test-lead 
40  grammes,  and  borax-glass  as  required,  after  scorification 
commences,  gives  good  results. 

In  case  an  insufficient  quantity  of  lead  or  borax-glass  has 


124 


A   MANUAL    OF  PRACTICAL   ASSA  YING. 


Ore. 

Grammes  of 
Test  lead. 

Grammes  of 
Borax-glass. 

Remarks. 

Galena  

IS-J8 

up  to  o.  5 

Galena  with  blende 
and  pyrite  

2O—  35 

0.4—0  8 

Iron  pyrite         .      . 

30—  j.5 

o  3-0  8 

Arsenical  pyrite  .  .  . 
Gray  copper  ..... 

45-50 

35—48 

0.3-1.5 

O    3-O    5 

High   temperature.     Addition   of 
litharge  helps  assay. 
Low  temperature 

Blende 

ao—  A  c 

o  3—0  6 

High    temperature      Addition    of 

Copper     ores     and 
mattes              . 

'IC—  JO 

o  3—  o  5 

oxide  of  iron  helps  assay. 

Lead  mattes  

VC-T.C. 

O.5—  I    O 

the  button  should  be  rescorified 
with  lead. 

Furnace  accretions. 
Tellurides  

25-50 
CQ 

0.3-1.5 

o.  3 

Add   a  cover  of  litharge  and  re~- 

Silicious  

25-3O 

scorify  the  button. 

Basic  

25—  3O 

O.5—  2   O 

If  the  ore  contains  much  lime  or 

Basic  with  Barium 
sulphate  .... 

25—  3O 

O    5—1    5 

magnesia  the  addition  of  sodium 
carbonate  helps  the  assay. 

Addition     of     sodium     carbonate 

Lead  carbonate.  .  .  . 
Speisse  

10-15 

3O-6O 

up  to  0.5 

O   3-O   5 

helps  the  assay. 
High  temperature       Rescorify  the 

button  with  lead  if  necessary. 

been  added,  the  deficiency  can  be  made  up  by  adding,  after 
the  scorification  has  commenced,  lead  in  the  form  of  sheet-lead 
rolled  into  a  compact  piece,  or  borax-glass  wrapped  in  a  small 
piece  of  tissue-paper.  If  the  test-lead  or  sheet-lead  contains 
silver  (some  silver  is  always  present),  the  amount  which  it 
contains  should  be  determined,  and  the  amount  present  in  the 
weight  of  test-lead  or  sheet-lead  used  in  the  assay  should  be 
deducted  from  the  weight  of  the  resultant  button. 

To  determine  the  silver  in  the  test-lead,  scorify  100  grammes. 
of  test-lead  with  borax  and  cupel  the  resulting  button. 


GOLD  AND    SILVER.  125 

Care  should  be  exercised  to  use  the  proper  amount  of 
fluxes,  so  that  the  resulting  button  will  be  of  the  proper  size 
(8  to  12  grammes  in'weight).  If  the  button  is  too  large,  it  may 
be  reduced  to  the  proper  size  by  further  scorification  with  test- 
lead  and  borax-glass.  This  will  frequently  happen  with  ores 
containing  much  copper.  It  is  better  to  reduce  too  large 
a  button  by  scorification  rather  than  to  cupel  the  button 
directly,  as  the  loss  of  precious  metals  is  less  in  scorification 
than  in  cupellation.  In  case  the  button  is  hard  or  brittle,  it 
should  be  rescorified,  with  the  addition  of  test-lead.  In  this 
case  care  should  be  exercised  in  removing  the  button  from  the 
slag  that  no  particles  of  the  button  be  lost.  The  fluxes  are 
usually  measured  in  place  of  weighing  them  out.  A  very  con- 
venient tool  for  measuring  out  the  test-lead  is  the  adjustable 
measure  which  sportsmen  use  for  measuring  the  charges  of 
shot  with  which  they  load  shells.  After  some  experience  the 
assayer  will  be  able  to  guess  at  the  weight  of  the  borax-glass 
sufficiently  close. 

One  half  of  the  test-lead  is  placed  in  the  scorifier,  the  care- 
fully weighed  ore  added  and  mixed  with  the  lead  by  means  of 
a  steel  spatula.  The  balance  of  the  test-lead  is  now  added  as 
a  cover  and  the  borax-glass  placed  on  top.  The  scorifiers  are 
placed  in  the  muffle  and  the  door  closed.  The  door  is  kept 
closed  until  scorification  commences,  which  is  indicated  by  the 
mass  subsiding  and  a  ring  of  slag  forming  around  the  surface 
of  the  metallic  lead.  As  the  scorification  proceeds  the  ring  of 
slag  grows  larger,  until  it  finally  closes  over  the  surface  of  the 
lead.  The  muffle  should  now  be  closed  and  the  heat  raised  for 
a  few  minutes,  in  order  to  insure  the  slag  being  perfectly  fluid  ; 
the  scorifier  is  then  removed  from  the  muffle  and  its  contents 
poured  into  the  scorifier  mould.  As  soon  as  the  assay  is  cool, 
which  takes  but  a  few  minutes,  it  is  removed  from  the  mould 
and  the  slag  removed  by  pounding  on  the  anvil  with  a  light 
hammer.  The  lead  button  is  hammered  into  the  form  of  a 
cube,  when  it  is  ready  for  cupellation.  The  slag  should  be 
perfectly  fluid.  The  lead  should  collect  in  one  malleable  but- 
ton. The  buttons  should  be  weighed  separately,  and  should 


126  A    MANUAL    OF  PRACTICAL  ASSAYING. 

not  differ  by  more  than  0.5  oz.  per  ton  on  ore  assaying  100  oza. 
per  ton. 

The  calculation  of  results  is  as  follows :  Suppose  T^  A.  T. 
taken  for  each  scorification,  four  scorifications  being  made. 
The  combined  weights  of  the  four  buttons  before  parting  is 
42.5  milligrammes.  The  weight  of  the  gold  button  from  the 
four  assays  is  3.8  milligrammes:  then  42.5  —  3.8  =  38.7  — 
weight  of  silver,  and  38.7  X  *£-  =96.75  oz.  silver,  and  3.8  X  -£ 
=  9.5  oz.  gold  per  ton  of  2000  Ibs.  If  the  gold  is  determined 
separately  by  crucible-assay  it  is  unnecessary  to  part  the  buttons 
from  the  scorification-assay,  except  as  a  check.  In  order  to 
obtain  the  weight  of  the  silver,  the  amount  of  gold  as  found 
by  crucible-assay  is  deducted  from  the  amount  of  silver  and 
gold  as  shown  by  the  scorification-assay. 

Crucible-assay. — The  amounts  of  ore  usually  taken  for 
assay  is  -J  A.  T.  or  I  A.  T.,  depending  upon  the  grade  of  the 
ore,  the  size  of  the  crucibles,  and  whether  the  fusion  is  per- 
formed in  the  wind-furnace  or  the  muffle-furnace.  If  the  fusion 
is  performed  in  the  muffle-furnace  J  A.  T.  will  usually  be  taken, 
as  a  larger  quantity  would  involve  the  use  of  an  awkward-sized 
crucible  for  the  muffle.  In  Colorado  the  fusion  is  usually  per- 
formed in  the  muffle,  and  this  practice  is  to  be  recommended 
on  account;  of  the  cleanliness  and  the  greater  facility  with  which 
the  heat  can  be  regulated  as  compared  with  fusion  in  the  wind- 
furnace. 

In  making  up  a  charge  the  object  to  be  attained  is  to 
produce  a  fluid  slag  which  will  permit  of  a  perfect  separation 
of  the  lead  into  a  button  of  the  proper  weight  (10  to  20 
grammes),  to  drive  the  impurities  in  the  ore  into  the  slag  and 
not  into  the  lead,  and  to  collect  all  the  gold  and  silver  in  the 
lead  button.  The  proper  fluxes  and  the  amounts  of  each  to  be 
added  will  depend  upon  the  mineral  composition  of  the  ore. 

If  the  ore  is  in  lump  form  its  mineral  composition  can  be 
determined  by  simple  eye-inspection  or  a  few  blowpipe  tests. 
If  in  the  form  of  powder,  place  about  0.2  gramme  of  the  ore  on 
a  large  watch-glass,  add  water,  and  van  by  rotating  and  tapping 
the  glass  to  separate  the  different  minerals.  An  inspection  of 


GOLD   AND    SILVER.  12 f 

the  vanned  sample  with  a  magnifying-glass  will  usually  shovr 
the  mineral  composition. 

In  making  up  a  charge  it  must  be  remembered  that  sulphur, 
arsenic,  and  antimony  act  as  reducing  agents,  and  that  ferric 
oxide  and  carbonate  act  as  oxidizing  agents.  Nitre  acts  as  an 
oxidizing  agent,  but  its  use  is  objectionable  for  the  following 
reasons :  Unless  a  large-sized  crucible  is  used,  and  care  is  exer- 
cised to  heat  the  crucible  and  its  contents  gradually,  during 
fusion  loss  is  liable  to  occur  from  deflagration  and  the  contents- 
of  the  crucible  boiling  over.  The  use  of  nitre  also  requires  that 
the  reducing  power  of  the  ore  be  known.  If  the  composition 
of  the  ore  is  known  (as  regards  S,  As,  and  Sb),  its  reducing 
power  can  be  calculated.  If  its  composition  is  unknown,  its 
reducing  power  may  be  determined  by  making  a  fusion,  using 
the  following  charge:  Ore,  2  gms.  ;  litharge,  15  gms.  ;  sodium 
bicarbonate,  10  gms.  Fuse  in  a  hot  fire,  and  when  the  fusion  is 
quiet  remove  the  crucible  from  the  fire,  pour  its  contents  into 
a  mould,  and  when  cool  detach  the  lead  button  from  the  slag 
and  weigh  it.  From  the  weight  of  the  lead  button  calculate 
the  amount  of  nitre  necessary  to  add  to  the  assay  to  obtain  a 
lead  button  of  the  proper  weight. 

Most  assayers  prefer  the  use  of  iron  nails  in  the  assay  of 
sulphides  and  arsenides  rather  than  the  use  of  nitre.  .Powdered 
argols,  flour  or  powdered  charcoal  are  the  usual  reducmg  agents 
used.  The  fusion  is  performed  in  either  the  wind-  or  muffle- 
furnace,  and  requires  from  25  to  40  minutes.  When  the  fusion 
is  quiet,  the  assay  should  be  allowed  to  remain  in  the  furnace 
for  a  few  minutes  at  a  strong  heat  before  it  is  withdrawn. 
When  the  assay  is  cool,  the  lead  button  is  extracted  from  the 
slag  in  the  same  manner  as  in  the  scorification-assay. 

The  lead  button  should  weigh  from  8  to  18  grammes  when 
J  A.  T.  to  I  A.  T.  of  ore  is  taken,  the  weight  depending  some- 
what upon  the  richness  of  the  ore.  Should  the  lead  button  be 
hard  (due  to  copper)  or  brittle  (due  to  As,  Sb,  Te,  etc.),  or 
should  a  button  of  matte  or  speiss  be  formed,  it  should  be 
scorified,  with  the  addition  of  test-lead  or  borax,  if  necessary,. 


128  A    MANUAL    OF  PRACTICAL   ASSAYING. 

before  cupellation.     The  lead  button   is   finally  cupelled,  the 
silver-gold  button  weighed,  and  parted  as  described  before. 

In  the  case  where  gold  only  is  determined  by  the  crucible- 
assay,  it  is  usual  to  add  silver  to  the  charge  before  fusion,  either 
in  the  form  of  pure  silver  foil  or  a  small  crystal  of  silver  nitrate, 
unless  the  ore  is  known  to  contain  sufficient  silver  to  insure 
parting.  The  charge  should  always  contain  an  excess  of 
litharge,  as  it  serves  as  an  excellent  flux  and  renders  the  slag 
fluid.  The  litharge  used  should  be  thoroughly  sampled  and 
the  silver  which  it  contains  determined.  A  good  charge  for 
this  purpose  is  :  Litharge,  2  A.  T.  ;  sodium  bicarbonate, 
i  A.  T. ;  argol,  I  gm.  The  amount  of  silver  which  the 
litharge  used  in  each  assay  contains  should  be  deducted  from 
the  result  of  the  assay.  The  crucibles  should  never  be  more 
than  three-fourths  filled,  and  in  case  nitre  is  used  not  over  two- 
thirds. 

The  assays  are  usually  made  in  duplicate,  and  the  buttons 
should  agree  within  0.5  oz.  silver  per  ton  on  ore  assaying  100 
oz.  per  ton.  The  results  in  gold  should  agree  almost  exactly. 
For  gold  assays  by  this  method  the  general  practice  is  to  run 
two  assays  of  \  A.  T.  of  ore  each,  and  part  the  buttons  together. 
In  the  case  of  rich  ores  the  buttons  are  parted  separately  as  a 
check.  The  table  on  the  following  page  gives  the  charges  for 
different  ores. 

In  the  case  of  copper,  iron,  and  arsenical  pyrites  it  is  prefer- 
able to  roast  the  ore  previous  to  assay.  After  roasting,  the 
ore  is  treated  as  an  oxidized  ore.  To  roast,  weigh  out  -J  A.  T. 
of  the  ore,  introduce  into  a  clay  roasting-dish  and  roast  in  the 
muffle,  stirring  from  time  to  time.  The  addition  of  ammonium 
carbonate  (commercial  salt)  facilitates  the  roasting. 

The  special  method  (see  Part  III,  Chapter  IV)  is  especially 
adapted  to  the  assay  of  pig  copper,  copper  mattes,  copper  and 
arsenical  pyrites,  etc. 

Cupellation. — Cupellation  is  performed  in  a  small  cupel 
made  of  powdered  and  sifted  bone-ash.  In  making  up  the 
cupels  the  addition  of  a  small  amount  of  potassium  carbonate 
to  the  water  used  to  moisten  the  bone-ash  aids  in  making  it 


GOLD  AND   SILVER. 


I29 


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glass. 
Special  method.  If  oxide  iron 
present,  add  soda  in  proportu 

If  gangue  is  oxide  or  carbonate 
iron  add  2  to  3  gms.  of  argol. 
Borax-glass  may  be  substituted 
some  of  the  silica. 

1 
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Litharge  is  added  according  to  1 
lead  contents  of  the  ore. 
Litharge  added  according  to  t 
lead  contents  of  the  ore. 

Collect  matte,  if  any,  and  scor 
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5? 

ISO  A   MANUAL   OF  PRACTICAL  ASSAYING. 

adherent.  The  cupel  should  always  weigh  a  little  more  than 
the  lead  button  to  be  cupelled.  A  very  convenient  size  is  a 
cupel  weighing  18  gms.  The  cupels  should  be  dried  for  a^  few 
days  before  using,  /  of  2  / 

The  cupels  are  placed  in  the  muffle  and  allowed  to  become 
hot  before  introducing  the  lead  button.  The  cube  of  lead  is 
dropped  into  the  cupel  and  the  door  of  the  muffle  closed  until 
cupellation  commences.  As  soon  as  cupellation  begins,  indi- 
cated by  the  surface  of  the  lead  becoming  bright  and  fumes 
arising  from  the  cupel,  the  door  of  the  furnace  is  opened.  The 
temperature  should  be  controlled  within  rather  narrow  limits. 
If  the  temperature  is  too  low  there  will  be  a  considerable  loss 
of  silver  and  a  liability  of  the  button  "  freezing  "  (solidifying), 
when  the  assay  is  ruined,  as  it  is  not  safe  to  accept  the  results 
from  a  frozen  button.  If  the  temperature  is  too  high  there 
will  be  a  considerable  loss  of  silver  by  oxidation  and  also  prob- 
ably a  mechanical  loss  in  the  lead  fumes.  The  proper  control 
of  the  temperature  can  be  learned  only  by  experience.  A  safe 
rule  is  to  have  the  cupels  show  a  slight  ring  of  litharge  crystals 
(feather  litharge)  around  the  edges.  As  the  cupellation  pro- 
ceeds the  lead  is  oxidized,  part  being  absorbed  by  the  cupel 
and  part  passing  off  in  fumes.  Just  before  the  last  traces  of 
lead  are  removed  the  button  will  exhibit  a  play  of  colors, 
owing  to  a  thin^film  of  litharge  on  the  surface.  At  this  point 
the  temperature  should  be  quite  high  in  order  to  insure  the 
removal  of  all  the  lead.  This  is  usually  accomplished  by  push- 
ing the  cupel  back  in  the  muffle.  When  the  lead  is  all  re- 
moved the  play  of  colors  ceases,  the  button  "brightens"  or 
"  winks "  and  solidifies.  The  cupel  should  be  allowed  to  re- 
main in  the  furnace  for  a  few  minutes  (there  is  no  loss  of  silver 
after  the  button  solidifies),  when  it  is  removed  and  cooled  pre- 
vious to  weighing.  If  the  button  of  silver  is  large  it  is  best  to 
cover  it  with  a' hot  cupel  before  removing  from  the  muffle,  and 
remove  it  gradually,  otherwise  the  button  is  liable  to  spit  or 
sprout,  which  may  occasion  loss.  ,It  is  never  safe  to  accept  a 
sprouted  button. 

The  button,  when  cold,  is  removed  from  the  cupel  by  a 


GOLD   AND   SILVER.  131 

pair  of  nippers,  squeezed  slightly  in  the  nippers,  and  its  bottom 
brushed  with  a  stiff  bristle-  or  wire-brush,  when  it  is  ready  for 
weighing. 

The  weighing  of  the  gold-silver  button  is  performed  on  a 
button-balance,  which  should  weigh  accurately  to  within  o.io 
milligramme.  In  the  case  of  small  buttons  and  where  -^ 
A.  T.  is  taken  for  assay,  the  balance  used  should  be  the  gold 
balance,  and  should  weigh  to  within  o.oi  milligramme.  The 
weight  of  the  gold-silver  button  being  noted,  the  button  is 
ready  for  parting. 

Parting. — Prior  to  parting  it  is  best  to  flatten  the  button  by 
a  few  light  blows,  especially  if  it  contains  much  gold.  In  order 
that  the  button  will  part  it  should  contain  at  least  two  and  one 
half  times  as  much  silver  as  gold.  If  the  button  does  not  con- 
tain sufficient  silver  to  insure  parting,  pure  silver  in  the  shape 
of  foil  is  added  on  a  cupel  and  fused  by  means  of  the  blowpipe 
flame.  After  alloying,  the  button  is  flattened  and  is  ready 
for  parting.  The  button  is  placed  in  a  small  porcelain  crucible 
and  c.  p.  nitric  acid  of  1.16  sp.  gr.  is  added.*  The  crucible  and 
its  contents  are  now  warmed  on  an  iron  plate  until  all  action 
of  the  acid  has  ceased,  when  the  solution  is  brought  to  a  boil. 
The  crucible  is  now  removed  from  the  plate  and  the  gold  col- 
lected in  one  mass  by  gently  rotating  and  tapping  the  crucible. 
The  solution  is  then  poured  off  and  fresh  acid  of  1.26  sp.  gr.  is 
added.  The  contents  of  the  crucible  are  now  boiled  for  three 
minutes,  the  gold  collected  in  one  mass,  and  the  acid  poured  off. 
The  gold  is  now  wrashed  three  times  with  hot  water,  and  the 
last  drops  of  water  removed  from  the  crucible.  A  convenient 
piece  of  apparatus  for  removing  the  last  drops  of  water  is  a 
piece  of  glass  tubing  drawn  to  a  fine  point  at  one  end.  The 
water  is  removed  by  suction  on  the  large  end  of  the  tube.  The 
crucible  is  now  warmed  on  the  iron  plate  until  thoroughly  dry, 
when  it  is  ignited  over  a  lamp  or  in  the  muffle.  The  gold 
should  be  bright,  and  have  the  characteristic  color  of  pure  gold 
The  gold  is  now  ready  for  weighing  on  the  gold  balance. 

*  Most  western  assayers  use  acid  of  only  one  strength  having  a  sp.  gr.  ot 
about  i. 20. 


132  A    MANUAL   OF  PRACTICAL   ASSAYING. 

Some  assayers  prefer  to  part  in  a  test-tube  or  small  parting 
matrice.  If  the  parting  is  done  in  a  test-tube  or  matrice  the 
tube  is  rinsed  out  twice  with  warm  distilled  water,  and  then 
filled  with  water  and  inverted  over  a  small  porcelain  crucible. 
When  the  gold  has  all  settled  to  the  bottom  of  the  crucible 
the  tube  is  removed,  the  water  poured  off,  and  the  gold  dried, 
ignited,  and  weighed  as  before. 

The  only  exception  to  the  above  methods  is  in  the  case  of 
an  ore  containing  metallic  scales.  Such  ores  should  be  assayed 
by  the  special  method  described  in  Part  III,  Chapter  VIII. 

On  the  Pacific  coast  the  fusion  for  the  assay  of  low-grade 
gold  ores  is  usually  performed  in  the  crucible  or  wind-furnace, 
from  2  A.  T.  to  4  A.  T.  of  ore  being  taken.  This  method  pre- 
sents the  advantages  that  large  quantities  of  ore  are  taken  for 
assay,  and  that  only  one  fusion  is  necessary  for  each  assay 


CHAPTER  VIII. 
MERCURY  (Hg). 

THE  wet  methods  for  the  determination  of  mercury  are 
extremely  tedious,  and  at  the  same  time  far  from  accurate, 
unless  extreme  precautions  are  observed. 

The  distillation  methods,  as  described  by  Fresenius,  Rick- 
etts,  Mitchell,  etc.,  are  good,  and  are  to  be  recommended 
where  the  percentage  of  mercury  present  is  large. 

The  two  following  methods  have  been  tested  and  proved 
to  be  accurate,  and,  as  they  are  simple  and  rapid,  are  to  be 
recommended,  especially  when  the  percentage  of  mercury 
present  is  small.  They  both  depend  upon  the  distillation  of 
the  mercury  and  catching  it  on  gold  in  the  form  of  amalgam.* 

First  Method. — Mix  from  0.2  to  2.0  grammes  of  ore  with 
from  i  to  4  grammes  of  iron  filings  (iron  filings  are  preferable 
to  lime,  as  they  render  the  mass  porous  and  facilitate  the 
distillation)  in  a  porcelain  crucible  of  sufficient  size.  Prepare 
a  cover  for  the  crucible  of  sheet  gold.  This  cover  should  be 
made  in  the  form  of  a  dish,  so  that  it  can  be  kept  cool  by 
keeping  it  filled  with  water.  It  should  be  of  a  diameter  some- 
what larger  than  the  diameter  of  the  crucible,  so  that  its  sides 
project  over  the  outer  rim  of  the  crucible.  The  weight  of  such 
a  cover  will  be  from  7  to  10  grammes. 

Place  the  crucible  in  the  ring-stand,  fit  on  the  cover,  and  fill 
it  with  cold  water.  Now  heat  the  crucible  gradually  with  the 

*  Silver  suggests  itself  as  a  substitute  for  gold,  but  as  the  author  has  never 
tried  silver  he  cannot  recommend  it. 

133 


134  A   MANUAL    OF  PRACTICAL  ASSAYING. 

flame  of  a  Buhsen  burner,  care  being  taken  to  keep  the  upper 
part  of  the  crucible  cool,  and  to  especially  keep  the  gold  cover 
cool.  The  first  can  be  accomplished  by  allowing  the  flame 
to  play  only  around  the  bottom  of  the  crucible,  care  being 
taken  to  never  allow  it  to  reach  the  upper  sides ;  and  the 
second  by  adding  cold  water  to  the  cover  from  time  to  time. 
It  will  require  from  10  to  30  minutes  to  distil  off  all  the 
mercury.  When  the  distillation  is  completed  remove  the  gold 
cover,  pour  off  the  water,  dry  carefully,  and  weigh.  The  in- 
crease in  weight  of  the  gold  cover  (it  having  been  dried  and 
weighed  before  the  operation)  represents  the  mercury. 

Second  Method. — This  method  is  essentially  the  same  as 
the  above,  the  form  of  apparatus  used  only  being  different. 

Prepare  a  piece  of  combustion-tubing  about  14  inches  long 
and  closed  at  the  left-hand  end.  Introduce  a  weighed  quantity 
of  the  ore,  which  should  be  mixed  with  iron  filings  and  lime, 
into  the  tube,  shaking  it  down  into  the  closed  end.  On  top  of 
the  ore  place  a  plug  of  ignited  asbestos.  Into  the  right-hand 
end  of  the  combustion-tube  introduce  a  spiral  of  gold-foil  of 
which  the  weight  has  previously  been  determined,  and  a  rubber 
cork  connected  with  a  small  glass  tube.  This  small  tube 
should  be  about  18  inches  in  length,  and  should  be  bent  up  in 
the  form  of  an  L  at  the  open  or  right-hand  end.  It  can  be 
kept  cool  by  wrapping  around  it  a  cloth  saturated  with  cold 
water.  This  second  small  tube  is  to  catch  any  mercury  which 
might  pass  the  gold-foil  and  not  be  caught  by  it. 

After  the  apparatus  is  connected  up,  heat  the  left-hand 
end  of  the  tube  containing  the  ore,  to  drive  off  the  mercury, 
gradually  raising  the  temperature,  but  keeping  the  right-hand 
end  of  the  tube  containing  the  gold  spiral  cool.  Should 
any  mercury  condense  in  the  combustion-tube  it  can  be  driven 
forward  by  moving  the  flame  of  the  burner  towards  the  right. 
After  all  of  the  mercury  is  distilled  off,  which  will  require  from 
10  to  30  minutes'  heating,  remove  the  heat,  and  allow  the  tube 
to  cool.  When  cool  disconnect  the  apparatus,  examine  the 
small  tube,  and  if  it  contains  no  mercury  remove  the  gold  spiral, 
and  weigh.  The  increase  in.  weight  of  the  gold  will  represent 


MERCURY.  135 

the  mercury.  Should  there  be  any  mercury  collected  in  the 
small  tube,  which  will  seldom  happen  if  the  operation  was 
properly  conducted,  it  must  be  collected  and  weighed,  its 
weight  being  added  to  the  weight  of  mercury  caught  by  the 
gold  spiral. 

This  process  properly  performed  will  give  excellent  results. 


CHAPTER  IX. 
LEAD  (Pb). 

NUMEROUS  methods  have  been  proposed  for  the  determina- 
tion of  lead,  both  volumetrically  and  gravimetrically,  but  the 
following  are  the  only  ones  which  are  extensively  used : 

1.  Fire-assay; 

2.  Gravimetric  determination  as  lead  sulphate,  and  weigh- 
ing as  such  ; 

3.  Volumetric  determination  with  a  standard  solution  of 
potassium  ferrocyanide ; 

4.  Volumetric  determination  with  a  standard  solution  of 
potassium  permanganate; 

5.  Volumetric  determination  with  a  standard  solution  of 
ammonium  molybdate. 

The  first  method  is  generally  used  in  the  United  States  and 
elsewhere  for  the  determination  of  lead  in  purchasing  ores. 
Its  advantages  are  :  Rapidity,  ease, of  execution,  and  the  large 
number  of  assays  which  may  be  made  in  a  given  time.  Its 
disadvantages  are :  All  the  lead  is  seldom  reduced,  and  the 
buttons  are  seldom  pure.  If  the  ore  contains  Sb,  Sn,  Bi,  Cu, 
Fe,  and  Zn,  the  button  is  liable  to  contain  more  or  less  of  these 
impurities.  A  recent  analysis  of  the  buttons  resulting  from 
several  hundred  lead  determinations  at  one  of  our  large  smelt- 
ing works  showecl  the  buttons  to  only  contain  96  per  cent 
lead,  as  an  average.  The  method,  and  with  good  reason,  is 
gradually  giving  way  to  the  more  accurate  volumetric  methods. 
Some  chemists  now  use  the  volumetric  methods  on  mattes 
and  all  but  pure  ores. 

The  advantages  of  the  second  method  are  that  the  results 
obtained  are  extremely  accurate.  Its  disadvantages  are  :  Time 
and  nicety  of  manipulation  required. 

136 


LEAD.  137 

The  advantages  of  the  third,  fourth  and  fifth  methods  are 
rapidity  and  ease  of  execution.  The  disadvantage  of  the  fourth 
method  is  that  the  results  are  apt  to  be  a  trifle  low  on  account 
of  the  incomplete  precipitation  of  the  lead  as  oxalate,  but  for 
technical  purposes  it  leaves  but  little  to  be  desired.  The  fifth 
method  answers  all  requirements  for  technical  purposes  and  is 
at  present  extensively  used  in  the  West.  As  this  method  fails 
where  much  lime  is  present,  owing  to  the  precipitation  of  calcium 
molybdate,  in  such  cases  it  will  have  to  be  slightly  modified. 
A  good  method  to  follow  where  lime  is  present  is  to  proceed 
according  to  Knight's  method  up  to  the  point  of  precipitation 
of  the  lead  on  zinc.  Dissolve  the  precipitated  lead  in  dilute 
nitric  acid,  using  as  small  a  quantity  as  possible,  render  the  solu- 
tion alkaline  with  ammonia,  neutralize  with  acetic  acid,  and 
proceed  with  the  titration  as  usual. 

1.  Fire-assay. — The  general  practice  in  Colorado  is  as  fol- 
lows :  5  grammes  of  pulverized  ore  are  mixed  with  from  15  to 
20  grammes  of  lead  flux  in  a  clay  crucible,  a  cover  of  borax  is 
added,  and  the  fusion  made  in  a  muffle-furnace.     The  time  of 
fusion  with  a  good  fire  is  from  15  to  20  minutes.     In  the  case 
of  sulphide  or  base  ores  one  or  two  iron  nails  or  a  few  loops 
of  iron  wire  are  added  to  the  charge.     When  the  fusion  has 
become  quiet  the  crucible  is  allowed  to  remain  in  the  muffle 
from   I  to  5   minutes,  when  it  is  drawn  out  and  its  contents 
poured  into  a  scorifier-mould.     As  soon  as  cold  the  button  and 
slag  are  removed  from  the  mould,  and  the  button  extracted 
from  the  slag  by  pounding  with  a  hammer.      The  button  is 
pounded  out  thin  on  the  anvil,  and  should  be  soft  and  malle- 
able.    If  brittle   it  contains  Sb,  S,  etc.     If  hard   it  probably 
contains  Fe,  Cu,  etc.     The  slag  should  be  vitreous  and  brittle, 
and  should  not  contain  shots  or  globules  of  lead.     Duplicate 
assays  should  agree  to  within  about  0.5  per  cent. 

2.  Gravimetric    Method,   weighing   as    PbSO4.— Lead 
may  be  determined  in  its  ores  and  furnace-products  by  treating 
i.o  gramme  of  ore  with  7  to  10  cc.  of  strong  nitric  acid  in  a 
flask  or  beaker  of  about  250  cc.  capacity,  covered  with  a  watch- 
glass,  and  heating  until  the  violent  action  ceases  and  the  sul- 


138  A   MANUAL    OF  PRACTICAL   ASSAYING. 

phur  is  oxidized.  Then  add  10  cc.  of  dilute  sulphuric  acid  (50 
per  cent  strong  sulphuric  acid  and  50  per  cent  water),  and  boil 
until  the  nitric  acid  is  expelled  and  dense  white  fumes  of  sul- 
phuric anhydride  appear.  Then  cool,  dilute  cautiously  with 
about  50  cc.  of  water,  and  shake  in  the  flask  to  break  up  any 
clots  which  may  have  formed,  and  also  to  cause  the  basic  sul- 
phate of  iron  to  go  into  solution.  If  very  much  iron  is  present, 
as  in  the  case  of  mattes,  it  may  be  necessary  to  heat  the 
solution  in  order  to  dissolve  the  basic  sulphate  of  iron.  Then 
cool,  filter,  and  wash  the  residue,  containing  lead  sulphate  and 
gangue,  with  water  containing  I  per  cent  of  sulphuric  acid,  and 
then  with  about  40  cc.  of  alcohol.  Dissolve  the  lead  sulphate 
on  the  filter,  also  what  may  stick  to  the  sides  of  the  flask,  with 
a  slightly  acid  solution  of  ammonium  acetate,  made  by  adding 
acetic  acid  to  strong  ammonia  until  the  solution  is  slightly 
acid,  then  bringing  back  to  an  alkaline  state  with  dilute  am- 
monia, and  then  back  to  an  acid  state  with  a  few  drops  of 
acetic  acid.  The  solution  should  be  warm  when  used.  From 
two  to  three  washings  with  ammonium  acetate  will  be  neces- 
sary to  dissolve  all  of  the  lead  sulphate.  After  washing  with 
the  acetate  solution,  wash  with  warm  water.  The  lead  will 
now  all  be  in  solution  in  the  filtrate,  whilst  the  silica,  calcium 
sulphate,  etc.,  will  remain  behind  on  the  filter.  Acidify  the 
filtrate  with  an  excess  of  sulphuric  acid,  cool,  and  filter  off.  the 
sulphate  of  lead,  washing  as  before  with  a  I  per  cent  solution 
of  sulphuric-acid  water  and  afterwards  with  alcohol  in  order 
to  displace  the  sulphuric  acid.  The  filtrate  may  be  tested  for 
lead  by  adding  a  few  drops  of  hydrochloric  acid  and  passing  a 
current  of  sulphuretted  hydrogen  gas  through  it.  Should  any 
lead  sulphide  be  precipitated,  it  should  be  filtered  off  and  dis- 
solved in  a  small  quantity  of  nitric  acid.  Sulphuric  acid 
should  then  be  added,  and  the  nitric  acid  be  driven  off  by 
boiling.  The  lead  sulphate  thus  recovered  from  the  filtrate 
should  be  added  to  the  other  precipitate.  The  filter  and  its 
contents  are  then  dried  at  a  moderate  temperature  (not  above 
100°  C),  and  when  dry  transfer  the  contents  of  the  filter-paper 
as  completely  as  possible  to  a  clean  watch-glass  by  inverting  it 


LEAD.  139 

over  the  glass  and  working  it  with  the  fingers.  Then  burn  the 
filter  in  a  weighed  porcelain  crucible,  and  after  it  is  burned  and 
ignited  add  to  the  ash  a  few  drops  of  nitric  acid  (to  dissolve 
the  lead  reduced  to  metallic  lead  by  the  carbon  of  the  filter- 
paper)  and  warm,  then  add  two  or  three  drops  of  sulphuric 
acid,  evaporate  off  the  excess  of  acid,  brush  the  precipitate 
into  the  crucible  from  the  watch-glass,  and  ignite  all.  Cool, 
and  weigh  the  crucible  and  its  contents.  This  weight,  less  the 
known  weight  of  the  crucible  and  filter-ash,  will  be  the  weight 
of  the  lead  sulphate.  To  calculate  the  weight  of  the  lead, 
multiply  the  weight  of  the  lead  sulphate  by  0.68317. 

3.  Volumetrically,  by   Means   of  Standard   K4FeC6N6. 
— This  method,  while  not  new,*  has  lately  come  into  promi- 
nence^ and  is  highly  recommended.     Treat  0.5  to  I  gm.  of  ore 
in  the  same  manner  as  with  Alexander's  method,  and  filter  off 
and  wash  the  precipitated  lead  sulphate.    Wash  this  precipitate 
back  into  the  flask  or  beaker  with  a  minimum  amount  of  water, 
and  add  30  cc.  of  a  saturated  solution  of  ammonium  carbonate. 
Heat  quickly  to  boiling,  and  boil  at  least  one  minute  in  order 
to  decompose  any  calcium   sulphate  which  may  have  formed. 
It   is  essential  that  any   calcium   sulphate  present   should   be 
converted  into  a  carbonate,  as  otherwise   the  sulphate  would 
react    upon    the  dissolved    lead    and    thus  cause    low  results. 
Filter  and  wash  thoroughly  with  hot  water  containing  a  little 
ammonium  carbonate.     Dissolve  the  washed  carbonate  of  lead 
in  strong  c.  p.  acetic  acid,  dilute  to  about  180  cc.,  and  titrate 
with  the  standard   ferrocyanide  solution  in  the  same  manner 
as  described  for  zinc  (p.  207).     The  ferrocyanide  solution  should 
be  of  such  a  strength  that  each  cc.  will  precipitate  o.oi  gm.  of 
lead.     It  is  prepared  by  dissolving  14  gms.  of  c.  p.  potassium 
ferrocyanide  in  one  litre  of  water. 

4.  Volumetrically,  by  Means  of  Standard  KMnO4. — For 
ores  and  furnace-products  the  method  of  procedure  is  as  fol- 
lows:  Treat  from  0.5  to  i.o  gramme  of  the  material,  according 
to  its  richness,  with  from  8  cc.  to  15  cc.  of  strong  nitric  and 

*  Eng.  and  Min.  Jour.,  Vol.  XLIX,  p.  178,  Feb.  8,  1890.     Mining  Industry, 
Vol.  VI,  No.  1 6,  Apl.  1890. 

\  Jour.  Am.  Chem.  Society,  Oct.  1893. 


I4O  A   MANUAL   OF  PRACTICAL  ASSAYING. 

from  8  Cc.  to  15  cc.  of  strong  sulphuric  acids  in  a  casserole, 
cover  with  a  watch-glass,  and  heat  until  decomposition  is 
effected  and  fumes  of  sulphuric  anhydride  appear.  Remove 
the  casserole  from  the  heat  and  cool ;  when  cool,  gradually 
add  about  50  cc.  of  cold  water,  heat  to  boiling,  and  immediately 
filter.  Wash  well  with  boiling  water  acidified  with  sulphuric 
acid,  and  finally  with  plain  hot  water.  Rinse  the  insoluble 
residue  into  a  beaker  of  about  200  cc.  capacity,  using  not  more 
than  50  cc.  of  water  ;  add  5  cc.  of  concentrated  hydrochloric 
acid,  cover  with  a  watch-glass,  and  boil  for  5  minutes.  The 
sulphates  of  lead  and  lime  pass  into  solution. 

If  much  silica  and  barium  sulphate  is  present,  it'  is  best  to 
filter  and  wash  well  with  boiling  water.  The  filtration  must 
be  done  rapidly.  Small  quantities  of  silica  do  not  interfere, 
but  larger  quantities  prevent  the  subsequent  precipitation  of 
the  lead  in  one  spongy  mass. 

Dilute  the  solution  with  water  to  about  100  cc.,  keeping  it 
hot  but  not  boiling.  Add  two  grammes  of  granulated  zinc 
(free  from  lead)  to  the  solution,  when  the  lead  will  immediately 
begin  to  be  precipitated  as  a  metallic  sponge.  When  the 
action  of  the  acid  on  the  zinc  has  apparently  ceased  add  0.5 
gramme  more  of  zinc  and  allow  to  stand  for  5  minutes.  Now 
boil  the  solution,  and  add  10  cc.  of  concentrated  hydrochloric 
acid.  This  dissolves  the  remainder  of  the  zinc  very  quickly, 
and  when  the  reaction  is  completed  the  lead  sponge  will  be 
found  floating  on  the  surface  of  the  liquid.  Decant  the  solu- 
tion, wash  the  lead  sponge  with  cold  water,  and  press  it  out 
flat  with  the  finger.  Dissolve  it  in  i  cc.  of  concentrated  nitric 
acid  and  20  cc.  of  hot  water.  Add  a  slight  excess  of  sodium 
carbonate  (salt),  and  redissolve  the  precipitated  lead  carbonate 
by  the  addition  of  5  cc.  of  strong  acetic  acid.  Add  20  cc.  of 
95  per  cent  alcohol,  heat  the  solution  to  65°  C.,  and  precipitate 
the  lead  with  a  saturated  solution  of  pure  crystallized  oxalic 
acid.  The  lead  comes  down  immediately  as  a  dense  white 
crystalline  precipitate.  Stir  briskly  until  the  precipitate  settles, 
leaving  a  perfectly  clear  supernatant  liquid.  Filter  and  wash 
the  precipitate  three  times  with  a  hot  mixture  of  alcohol  and 


LEAD.  141 

water  (i  alcohol,  I  water),  and  then  four  times  with  hot  water 
alone.  In  washing  the  precipitate  it  is  well  to  use  a  fine  jet, 
keeping  the  stream  on  the  filter  and  not  allowing  it  to  flow  on 
the  glass,  as  otherwise  the  precipitate  is  liable  to  creep  up  on 
the  funnel  and  thus  occasion  loss.  When  thoroughly  washed, 
the  precipitate  is  rinsed  into  a  flask  or  beaker  with  about  50 
cc.  of  hot  water,  add  5  cc.  of  concentrated  sulphuric  acid  and 
determine  the  oxalic  acid  which  was  combined  with  the  lead 
in  the  same  manner  as  in  the  estimation  of  lime  volumetrically, 
using  a  standard  solution  of  potassium  permanganate.  (See 
Part  I,  Chap.  XXIII.) 

A  quite  dilute  solution  of  permanganate  should  be  used — 
not  stronger  than  1.58  grammes  of  KMnO4  to  1000  cc.  of  water. 
One  cc.  of  such  a  solution  will  be  equal  to  about  0.05  gin.  of 
lead.  The  standard  of  the  solution  in  terms  of  lead  is  obtained 
by  multiplying  the  standard  in  terms  of  oxalic  acid  by  1.6428. 

Bismuth  and  antimony  are  the  only  impurities  of  the  ores 
which  are  liable  to  affect  the  results.  By  adding  a  large  excess 
of  sulphuric  acid  to  the  nitric-acid  solution,  so  that  when  the 
evaporation  takes  place  and  the  sulphuric-acid  fumes  appear 
the  mass  will  be  in  a  fluid  and  not  a  pasty  condition,  and 
allowing  the  mixture  to  cool  and  adding  cold  water  gradually 
to  avoid  heating,  all  of  the  bismuth  goes  into  solution,  and 
remains  in  solution  for  a  sufficient  length  of  time  to  allow 
filtration  and  a  separation  of  the  sulphate  of  lead  to  be 
effected.  If  sufficient  sulphuric  acid  is  .used,  most  of  the  anti- 
mony will  likewise  be  held  in  solution.  Should  some  antimony 
remain  with  the  lead  sulphate,  it  will  be  reduced  to  the  metal- 
lic state  by  the  zinc,  and  when  the  solution  of  the  lead  is 
effected  with  the  nitric  acid  it  will  remain  behind  as  the  in- 
soluble oxide,  and  thus  be  eliminated. 

A  determination  may  be  effected  in  from  35  to  40  minutes. 

This  method  is  due  to  F.  C.  Knight.* 

According  to  Mr.  Knight's  results,  about  99.6  per  cent  of 
the  lead  present  is  obtained. 

A.  H.  Lowf  proposes  a  modification  of  Knight's  method 
which  presents  some  advantages. 

*  Proceedings  of  the  Colorado  Scientific  Society,  Nov.  7,  1892. 
f  Journal  of  the  Am.  Chem.  Society,  Oct.  1893. 

^"LIB/ 


142  A   MANUAL   OF  PRACTICAL  ASSAYING. 

5.  Volumetrically  by  Means  of  a  Standard  Solution  of 
Ammonium  Molybdate. — This  method  is  based  upon  the 
fact  that  ammonium  molybdate  when  added  to  a  hot  solution 
of  lead  acetate  will  produce  a  precipitate  of  lead  molybdate 
(PbMoO4)  which  is  insoluble  in  acetic  acid.  Any  excess  of 
ammonium  molybdate  will  give  a  yellow  color  with  a  freshly 
prepared  solution  of  tannin.  The  solution  of  tannin  is  made 
by  dissolving  one  gramme  of  tannin  in  300  cc.  of  water,  and  is 
used  as  an  indicator  on  a  porcelain  plate.  The  standard  solu- 
tion of  ammonium  molybdate  is  prepared  by  dissolving  9 
grammes  of  the  salt  in  1000  cc.  of  water.  This  should  give  a 
solution  of  which  I  cc.  is  equal  to  about  o.oi  gm.  of  lead.  If 
the  solution  is  not  clear,  it  can  be  clarified  by  adding  a  few 
drops  of  ammonium  hydrate. 

To  standardize  the  molybdate  solution  weigh  out  0.3  gm. 
of  pure  lead  sulphate  and  dissolve  it  in  hot  ammonium  acetate  ; 
acidify  the  solution  with  acetic  acid  and  dilute  with  hot  water 
to  250  cc.  Heat  to  boiling,  and  add  from  a  burette  the  molyb- 
date solution  until  all  the  lead  is  precipitated  as  a  white  pre- 
cipitate. This  is  ascertained  by  placing  the  drops  of  tannin 
solution  on  a  porcelain  plate  and  adding  drops  of  the  solution 
in  the  beaker  to  the  tannin  drops  from  time  to  time.  As  long 
as  the  lead  is  in  excess  no  color  is  produced,  but  as  soon  as  the 
molybdate  is  in  excess  a  yellow  color  is  produced  (0.3  gm. 
PbSO4  X  0.68317  =  0.20495  gm.  Pb).  This  operation  should 
be  repeated,  and  from  the  number  of  cc.  of  the  molybdate 
solution  used  in  each  case  the  value  of  one  cc.  is  calculated  in 
the  usual  way. 

To  determine  the  lead  in  an  ore-  or  furnace-product  by  this 
method  0.5  or  i.o  gm.  of  substance  is  weighed  out  (according  to 
the  percentage  of  lead:  if  30  per  cent  or  over,  0.5  gm.  will  be 
sufficient)  and  decomposed  in  a  casserole  by  heating  with  15 
cc.  of  strong  nitric  and  10  cc.  of  strong  sulphuric  acids.  When 
the  nitric  acid  is  completely  expelled,  which  is  indicated  by 
fumes  of  sulphuric  anhydride,  the  casserole  is  removed  from 
the  heat  and  its  contents  cooled.  Dilute  with  cold  water,  stir 
thoroughly,  and  boil  until  all  soluble  sulphates  are  dissolved. 


LEAD.  143 

Now  filter,  leaving  as  much  of  the  precipitate  in  the  casserole 
as  possible,  and  wash  twice  with  hot  dilute  sulphuric  acid  and 
once  with  cold  water.  Now  add  to  the  sulphate  of  lead  re- 
maining in  the  casserole  hot  ammonium  acetate,  pour  the  hot 
solution  on  the  filter,  and  allow  it  to  run  through  into  a  clean 
beaker.  This  operation  is  repeated  until  the  sulphate  of  lead 
is  completely  dissolved.  Now  wash  out  the  casserole  thoroughly 
with  hot  water  into  the  filter.  Acidify  the  solution  in  the 
beaker  with  acetic  acid,  dilute  up  to  250  cc.  with  hot  water, 
and  heat  to  boiling.  Run  in  from  the  burette  the  standardized 
solution  of  ammonium  molybdate  until  all  the  lead  is  precipi- 
tated, stirring  thoroughly  after  each  addition  of  the  molybdate, 
and  testing  a  drop  of  the  solution  from  time  to  time  on  the 
porcelain  plate  with  the  tannin  solution.  From  the  number  of 
cc.  of  the  molybdate  solution  used  calculate  the  per  cent  of 
lead. 

Arsenic,  antimony,  and  phosphorus  do  not  interfere  with 
the  method,  as  they  pass  through  the  filter  into  solution. 

A  determination  can  readily  be  made  in  thirty  minutes. 

The  method  is  largely  used  in  Colorado  for  the  determina- 
tion of  lead  in  ores  containing  copper,  and  in  both  lead  and 
copper  mattes.  The  results  are  excellent.* 

This  method  is  due  to  H.  H.  Alexander. f 

*  State  School  of  Mines  Scientific  Quarterly,  Vol.  I,  No.  4. 

t  The  Engineering  and  Mining  Journal,  Vol.  LV,  No.  13,  April  I,  1893. 


CHAPTER  X. 

ARSENIC  (As). 

FOR  the  technical  estimation  of  arsenic  in  ores  and  metal- 
lurgical products,  the  following  method,  which  was  devised  and 
published  by  Dr.  Richard  Pearce,  of  Denver,  Colo.,*  is  the 
most  rapid  and  at  the  same  time  one  of  the  most  accurate 
methods  which  we  have  : 

The  finely  powdered  substance  for  analysis  is  mixed  in  a 
platinum  crucible  with  from  six  to  ten  times  its  weight  of 
a  mixture  of  equal  parts  of  sodium  carbonate  and  potassium 
nitrate.  The  mass  is  then  heated  with  gradually  increasing 
temperature  to  fusion  and  allowed  to  remain  for  a  few  minutes 
in  that  state.  It  is  then  allowed  to  cool,  and  the  mass  removed 
by  the  addition  of  warm  water.  It  is  best  to  remove  the  mass 
by  warm  water,  pouring  in  to  acasserole,  and,  after  the  whole  is 
transferred  to  the  casserole,  to  heat  to  a  boiling  temperature  and 
filter.  The  arsenic  is  in  the  filtrate  as  an  alkaline  arseniate,  which 
is  then  acidified  with  nitric  acid  and  boiled  to  expel  carbonic 
acid  and  nitrous  fumes.  It  is  then  cooled  and  almost  exactly 
neutralized  as  follows :  Place  a  small  piece  of  litmus-paper  in 
the  liquid,  which  should  show  an  acid  reaction,  and  then  grad- 
ually add  ammonia  until  the  litmus-paper  turns  blue,  avoiding 
a  great  excess.  Again  make  slightly  acid  with  a  drop  or  two 
of  concentrated  nitric  acid,  and  then,  by  means  of  very  dilute 
ammonia  and  nitric  acid,  added  drop  by  drop,  bring  the  solu- 
tion to  a  condition  that  the  litmus-paper,  after  having  previ- 
ously been  reddened,  will  in  the  course  of  half  a  minute  begin 
to  turn  blue.  If  the  neutralization  has  caused  much  of  a  pre- 

*  Proceedings  of  the  Colorado  Scientific  Society,  Vol.  I. 

144 


ARSENIC.  145 

cipitate  (alumina,  etc.)  the  solution  is  best  filtered  at  once  in 
order  to  render  the  subsequent  washing  and  filtration  of  the 
arseniate  of  silver  more  rapid.  If  this  filtration  is  unnecessary, 
the  litmus-paper  is  drawn  up  the  sides  of  the  beaker,  leaving 
a  portion,  however,  yet  immersed  in  the  liquid.  A  neutral 
solution  of  nitrate  of  silver  is  now  added  in  slight  excess,  and 
after  stirring  the  color  of  the  immersed  portion  of  the  litmus- 
paper  is  noted,  and  if  necessary  the  neutralization  is  repeated. 
The  second  neutralization  is  always  necessary  when  the 
amount  of  arsenic  present  is  large,  as  nitric  acid  is  set  free  in 
the  reaction  between  the  alkaline  arseniate  and  silver  nitrate, 
according  to  one  or  both  of  the  following  equations,  or  those 
of  the  corresponding  potassium  salts : 

3AgN03  +  NaH2As04  =  Ag3AsO4  +  NaNO3  +  2HNO3, 
and 

3AgN03  +  Na2HAs04  =  Ag3AsO4  +  2NaNO3  +  HNO3. 

The  precipitated  arseniate  of  silver,  which  is  of  a  brick-red 
color,  is  finally  collected  on  a  filter,  and  well  washed  with  cold 
water.  As  a  further  precaution,  the  filtrate  may  be  tested  with 
silver  nitrate,  dilute  nitric  acid,  and  ammonia  to  see  if  the  pre- 
cipitation is  complete.  The  object  is  now  to  determine  the 
amount  of  silver  in  the  precipitate  of  arseniate  of  silver,  and 
from  this  to  calculate  the  arsenic.  This  may  be  accomplished 
in  two  ways :  First,  the  precipitate  may  be  dried  in  a  scorifier, 
test-lead  and  borax  added,  and  a  scorification-assay  made  to 
determine  the  amount  of  silver.  If  this  method  is  adopted  any 
soluble  chloride  must  be  removed  earlier  in  the  process.  Gen- 
erally but  few  ores  will  be  encountered  in  which  any  soluble 
chloride  is  present.  Another  and  shorter  method  of  determin- 
ing the  silver  is  as  follows :  Dissolve  the  arseniate  of  silver  on 
the  filter  with  dilute  nitric  acid  (which  leaves  undissolved  any 
silver  chloride)  and  titrate  the  filtrate,  after  addition  of  about 
5  cubic  centimetres  of  a  saturated  solution  of  ferric  ammonium 
sulphate,  with  a  standard  solution  of  ammonium  sulphocyanate 
(about  5  grammes  of  the  salt  to  the  litre  of  water),  run  in  until 


146  A   MANUAL   OF  PRACTICAL  ASSAYING. 

a  fairit-red  tinge  is  obtained,  which  remains  after  considerable 
shaking.  The  shaking  breaks  up  any  clots  of  sulphocyanate  of 
silver,  and  frees  any  solution  held  mechanically. 

From  the  formula  3Ag2O,  As2O5  we  find  that  648  parts  of 
silver  represent  1 50  parts  of  arsenic,  or  108  parts  of  silver  25 
parts  of  arsenic. 

In  determining  arsenic  in  ores  very  rich  in  arsenic,  such  as 
arsenopyrite,  niccolite,  etc.,  it  is  desirable  to  add  a  few  drops 
of  fuming  nitric  acid  to  the  weighed  sample  in  the  platinum 
crucible  prior  to  the  usual  fusion.  This  oxidizes  the  arsenic 
and  sulphur  present,  and  prevents  subsequent  loss  by  defla- 
gration ;  this  precaution  should  also  be  adopted  in  the  deter- 
mination of  arsenic  in  sulphide  of  arsenic  obtained  in  the 
ordinary  course  of  analysis.  Molybdic  and  phosphoric  acids, 
which  behave  similarly  to  arsenic  under  this  treatment,  inter- 
fere, of  course,  with  the  method.  Antimony,  by  forming 
antimoniate  of  sodium,  or  potassium,  remains  practically  in- 
soluble and  without  effect.  A  determination  can  be  made  in 
30  minutes  by  this  process.  A  modification  of  the  above 
method  has  been  proposed  by  R.  C.  Canby,*  in  which  he 
neutralizes  the  solution  with  an  emulsion  of  c.  p.  zinc  oxide. 
The  zinc  oxide  is  added  in  slight  excess  (see  Chapter  XX: 
manganese),  no  delicate  testing  with  litmus-paper  and  alter- 
nate adding  of  dilute  ammonia  and  nitric  acid  becomes  neces- 
sary, thus  saving  time.  The  slight  excess  of  zinc  oxide  also 
tends  to  -render  the  subsequent  filtration  and  washing  of  the 
arseniate  of  silver  more  rapid,  as  it  holds  the  gelatinous  silica 
which  is  precipitated  on  neutralization.  The  writer  has  tried 
this  method  of  neutralization,  and  regards  it  as  an  improve- 
ment on  the  method  as  originally  given. 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  Vol.  XVII, 
P- 77- 


CHAPTER  XI. 
ANTIMONY   (Sb). 

ANTIMONY  in  ores,  mattes,  etc.,  is  best  determined  by  one 
of  the  following  gravimetric  methods.  The  first  method  is  the 
most  accurate,  and  is  to  be  recommended  in  scientific  work  and 
where  great  accuracy  is  required.  The  second  method  is  more 
rapid  and  simpler  than  the  first,  and  answers  all  purposes  for 
technical  work. 

First  Method. — Precipitation  of  the  antimony  as  sulphide, 
conversion  of  the  sulphide  into  antimony  tetroxide  (SbaO4), 
and  weighing  as  such.  Method  due  to  Bunsen.* 

Second  Method. — Precipitation  of  the  antimony  as  metal- 
lic antimony,  and  weighing  as  such.  This  method  is  due  to 
Carnot.f 

First  Method. — Treat  i.o  gm.  of  finely  pulverized  ore  in  a 
flask,  similar  to  the  flask  used  in  the  determination  of  copper, 
with  5  cc.  of  concentrated  nitric  acid,  10  cc.  of  concentrated 
hydrochloric  acid,  and  3  gms.  of  crystallized  tartaric  acid. 
Heat  until  the  substance  is  nearly  dry,  in  order  to  expel  most 
of  the  free  acid.  To  the  nearly  dry  mass  add  100  cc.  of  water, 
make  alkaline  with  ammonia,  add  10  cc.  of  yellow  ammonium 
sulphide,  and  warm  gently  for  one  hour.  Sufficient  ammonium 
sulphide  should  be  added  to  render  the  fluid  yellow.  Filter, 
and  wash  with  hot  water  until  the  filtrate  runs  through  color- 
less. The  antimony  will  be  in  the  filtrate  as  ammonium  sulph- 
antimonate.  Acidify  the  filtrate  with  hydrochloric  acid  and 
allow  the  precipitate  to  settle.  Should  the  ore  be  not 
thoroughly  decomposed  by  the  above  treatment  with  acids,  dry 

*  Fresenius,  Quant.  Anal.,  §  125,  p.  243. 
\  Comptes  Rendus,  cxiv.  p.  587. 

147 


A   MANUAL   OF  PRACTICAL  ASSAYING. 

the  residue  remaining  on  the  filter,  and  fuse  it  with  5  gms.  of 
sodium  carbonate  and  i.o  gm.  of  sodium  nitrate.  Treat  the 
fused  mass  with  an  excess  of  hydrochloric  acid  and  i.o  gm.  of 
tartaric  acid,  evaporate  off  the  excess  of  acid,  add  25  cc.  of 
water,  render  alkaline  with  ammonia,  and  treat  with  yellow 
ammonium  sulphide.  Filter,  wash,  and  acidulate  the  filtrate 
with  hydrochloric  acid.  Allow  the  precipitated  antimony  sul- 
phide to  settle,  and  filter  off  the  precipitate  on  the  same  filter 
as  before  washing  with  hot  water.  Wash  finally  with  alcohol 
to  displace  the  water  adhering  to  the  precipitate,  dry  it  at  a 
low  heat,  wash  with  carbon  disulphide  to  dissolve  the  free 
sulphur,  and  dry  at  a  temperature  of  not  over  100°  C.  As 
soon  as  the  precipitate  is  dry  enough  to  remove  it  from  the 
filter,  brush  it  into  a  watch-glass,  cleaning  the  paper  as 
thoroughly  as  possible,  and  place  the  filter  in  a  large  covered 
porcelain  crucible  which  has  been  previously  weighed.  Moisten 
it  with  concentrated  nitric  acid,  add  4  to  5  cc.  of  red  fuming 
nitric  acid,  and  evaporate  on  a  water-bath  to  dryness.  Now 
transfer  the  precipitate  to  the  crucible  and  add  a  little  concen- 
trated nitric  acid  by  means  of  a  pipette,  inserting  the  point  of 
the  pipette  under  the  edge  of  the  lid.  When  the  violent  action 
has  ceased  add  10  times  the  volume  of  the  precipitate  of  red 
fuming  nitric  acid,  and  evaporate  to  dryness  on  the  water-bath, 
removing  the  cover  as  soon  as  all  danger  of  loss  by  spirting  is 
past.  Finally  ignite  cautiously  over  a  Bunsen  burner  to  expel 
the  sulphuric  acid  and  convert  the  antimony  into  tetroxide. 
Weigh  the  tetroxide  and  calculate  the  antimony.  The  weight 
of  the  precipitate  multiplied  by  0.78947  equals  the  weight  of 
antimony. 

In  very  accurate  work  all  the  filtrates  should  be  treated  with 
sulphuretted  hydrogen  to  recover  any  traces  of  antimony  which 
may  have  possibly  escaped. 

A  determination  requires  from  three  to  four  hours. 

Second  Method. — This  method  consists  essentially  in  obtain- 
ing the  antimony  in  a  hydrochloric-acid  solution,  in  precipitat- 
ing it  with  tin  and  weighing  it  in  the  metallic  state.  The 
method  varies  somewhat,  according  to  whether  the  ores  are 


ANTIMONY.  149 

oxidized  or  sulphide  ores,  and  according  to  whether  they  con- 
tain lead  or  not. 

Sulphides. — Take  from  2  to  5  gms.  of  ore,  according  to  its 
supposed  percentage  of  antimony,  so  that  we  may  operate  on 
about  i.o  gm.  of  antimony.  Treat  in  a  small  flask,  as  before, 
with  50  to  60  cc.  of  concentrated  hydrochloric  acid,  and  heat 
on  a  sand-bath.  When  the  acid  appears  to  have  no  further 
action  and  the  ore  is  decomposed,  decant  the  clear  liquid 
through  a  filter  and  add  a  fresh  quantity  of  acid.  Heat  again, 
and  continue  until  the  sulphides  are  thoroughly  decomposed. 
Decant  through  the  filter  and  renew  the  acid  once  more,  adding 
i  or  2  drops  of  nitric  acid  to  complete  the  attack ;  heat  at 
100°  C,  filter,  and  wash  the  insoluble  gangue  with  hydrochloric 
acid  diluted  with  water. 

The  combined  filtrates  are  diluted  with  an  equal  volume  of 
water,  a  blade  of  tin  is  introduced  and  the  solution  heated  to 
80°  or  90°  C.  The  precipitation  begins  immediately,  and  for 
i.o  gm.  of  antimony  is  completed  in  about  90  minutes. 

The  precipitate  is  washed  by  decantation,  replacing  the 
liquid  with  dilute  hydrochloric  acid  to  remove  salts  of  tin  and 
any  other  salts  which  may  be  present.  The  metallic  antimony 
is  brought  upon  a  weighed  filter,  washed  thoroughly  with  hot 
water,  and  finally  with  alcohol.  The  metallic  antimony  is  then 
dried  at  100°  C.  and  weighed  together  with  the  filter. 

If  the  operation  is  conducted  as  above  there  is  neither 
appreciable  loss  nor  oxidation. 

Oxidized  Ores. — The  oxides  of  antimony  are  frequently 
attacked  with  extreme  difficulty  by  hydrochloric  acid.  We  are 
then  exposed  either  to  notable  losses  by  volatilization  or  to  an 
incomplete  solution  of  the  antimony. 

The  method  of  procedure  is  as  follows :  The  ore  is  placed 
in  a  small  flat-bottomed  flask,  in  which  the  quantity  of  from  2 
to  5  gms.  forms  a  light  layer  permeable  to  gases.  Place  an 
elbow-tube  in  the  flask,  by  means  of  a  cork  in  the  neck,  so 
that  its  lower  end  descends  almost  to  the  level  of  the  ore. 
Through  the  tube  pass  a  current  of  dry  sulphuretted  hydro- 
gen, placing  the  flask  upon  a  piece  of  wire-gauze  at  the  height 


ISO  A   MANUAL   OF  PRACTICAL  ASSAYING. 

of  a  few  inches  above  the  flame  of  a  Bunsen  burner,  so  that 
the  temperature  shall  not  exceed  300°  C.,  producing  no  vola- 
tilization of  the  antimony  sulphide.  The  ore  remains  pulveru- 
lent and  is  permeated  by  the  hydrogen  sulphide,  which  acts  at 
the  same  time  as  a  reducing  and  ^sulphurizing  agent.  The 
surface  of  the  ore  is  renewed  from  time  to  time  by  shaking 
the  flask.  The  conversion  is  complete  in  about  one  hour. 
When  cold  the  ore  is  treated  with  hydrochloric  acid  in  the  same 
flask.  The  precipitation  and  weighing  are  then  effected  as 
described  above.  Experience  shows  that  the  quantity  of  anti- 
mony remaining  undissolved  is  quite  insignificant. 

Ores  containing  Iron  or  Lead. — Neither  the  presence  of 
iron  nor  of  zinc,  even  in  considerable  quantities,  interferes  with 
the  method. 

Lead,  if  present,  will  be  precipitated  with  the  antimony  by 
the  tin.  Its  presence  can  easily  be  detected.  If  present  weigh 
the  combined  precipitates  of  antimony  and  lead,  and  after 
weighing  heat  to  50°  or  60°  C.  in  a  solution  of  yellow  sodium 
sulphide  (prepared  by  boiling  the  monosulphide  with  flowers  of 
sulphur).  The  antimony  is  rapidly  dissolved,  the  lead  being 
converted  into  a  sulphide  which  is  insoluble. 

Filter  off  the  lead  sulphide,  wash  thoroughly,  and  dry. 
Finally  ignite  the  precipitate  in  a  Rose  crucible  in  a  stream  of 
sulphuretted  hydrogen,  and  weigh.  Eighty-five  per  cent  of 
the  weight  of  this  lead  sulphide  represents  the  corresponding 
weight  of  the  metallic  lead,  which  is  to  be  deducted  from  the 
combined  weight  of  the  antimony  and  lead. 


CHAPTER   XII. 
TIN   (Sn). 

A  GREAT  many  methods  have  been  proposed  for  the  separa- 
tion and  estimation  of  tin,  for  which  see  Fresenius,  Rose, 
Cairns,  Crooks,  etc.  It  is  the  opinion  of  the  author  that  the 
following  methods  are  the  best  in  use : 

First  Method. — Fuse  i.o  gm.  of  very  finely  pulverized  rich 
ore  with  3  gms.  pf  sulphur  and  3  gms.  of  dry  sodium  carbonate 
in  a  large  porcelain  crucible  over  a  Bunsen  burner  for  about 
one  hour.  The  ore  and  flux  should  be  thoroughly  mixed.  The 
heat  should  not  be  too  great,  nor  should  the  fusion  be  too 
greatly  prolonged,  as  the  sulphide  of  tin  may  become  oxidized, 
and  consequently  be  insoluble  when  the  fusion  is  treated  with 
water.  The  fusion  results  in  the  production  of  sodium  and  tin 
sulphides.  If  the  fusion  has  been  properly  conducted  the  tin 
sulphide  should  go  into  solution,  upon  addition  of  water,  as 
sodium  sulpho-stannate. 

Allow  the  fusion  to  cool,  place  the  crucible  in  a  casserole, 
add  hot  water,  and  digest  on  the  water-bath  until  the  mass  is 
disintegrated  and  removed  from  the  crucible.  Filter,  wash 
thoroughly  with  hot  water,  and  acidulate  the  filtrate  with  sul- 
phuric acid  to  precipitate  the  tin  sulphide.  Allow  the  sulphide 
to  settle,  keeping  the  solution  warm  ;  pour  the  clear  solution  on 
a  filter,  wash  four  or  five  times  by  decantation,  and  finally  on 
the  filter,  using  hot  water.  Should  the  precipitate  run  through 
the  filter  wash  with  ammonium  acetate.  Place  the  filter  and  its 
contents  in  a  weighed  porcelain  crucible,  and  apply  a  very  gentle 
heat,  with  free  access  of  air  until  the  odor  of  sulphurous  acid  is 
no  longer  perceptible.  Gradually  increase  the  heat  to  a  high 

151 


152  A   MANUAL    OF  PRACTICAL  ASSAYING. 

degree,  and  finally  add  ammonium  carbonate  to  insure  the  com- 
plete elimination  of  the  sulphuric  acid.  The  treatment  with 
ammonium  carbonate  should  be  repeated  several  times.  A 
high  heat  at  the  beginning  is  to  be  avoided,  as  fumes  of  stannic 
-sulphide  are  liable  to  escape  if  the  heat  is  too  high. 

The  residue  from  the  first  fusion  and  solution  invariably 
contains  tin ;  hence  it  must  be  refused.  Before  fusion,  if  much 
iron  is  present  it  should  be  removed  with  a  little  dilute  hydro- 
chloric acid.  If  but  little  iron  sulphide  is  present  the  treat- 
ment with  acid  can  be  dispensed  with.  The  residue  is  now 
dried,  burned,  mixed  with  sodium  carbonate  and  sulphur,  and 
fused  as  before.  The  fused  mass  is  dissolved  in  water,  filtered, 
and  the  tin  precipitated  as  before.  The  weight  of  tin  recov- 
ered from  this  second  fusion  is  to  be  added  to  the  weight 
obtained  from  the  first  fusion.  If  the  fusions  were  properly 
conducted  a  third  fusion  will  generally  be  unnecessary.* 

After  weighing  the  stannic  oxide,  it  should  be  examined 
for  silica  as  follows :  Fuse  a  weighed  portion  with  three  or  four 
parts  of  a  mixture  of  equal  parts  of  sodium  and  potassium  car- 
bonates, treat  the  fused  mass  with  hot  water,  filter,  and  wash. 
Acidulate  the  filtrate  with  hydrochloric  acid,  and  should  any 
silica  separate  out,  filter  it  off,  reserving  the  filter  and  its  con- 
tents. Acidulate  the  filtrate  with  hydrochloric  acid  and  pass 
sulphuretted  hydrogen,  to  precipitate  the  tin.  Filter  out  the 
precipitated  sulphide  and  treat  the  filtrate  as  usual  for  silica, 
finally  filtering  through  the  reserved  filter.  Calculate  the  silica 
thus  found  to  the  whole  weight  of  stannic  oxide,  and,  after 
deducting  this  weight  from  the  weight  of  the  stannic  oxide 
and  silica,  calculate  the  metallic  tin.  This  method  is  due  to 
Rose.t 

Second  Method. — Of  all  the  different  methods  proposed 
for  the  dry  or  fire  assay  of  tin  ores  it  is  believed  that  the  fol- 
lowing is  the  best.  This  is  the  German  method,  and  is  essen- 
tially as  follows:^:  Mix  5  grammes  of  ore  with  i.o  gramme  of 

*  School  of  Mines  Quarterly,  Vol.  XIII,  No.  4,  p.  370. 

f  Quantitative  Analysis,  p.  393. 

\  Miller,  School  of  Mines  Quarterly,  Vol.  XIII,  No.  4,  p.  372. 


TIN,  153 

finely  ground  charcoal,  and  place  in  the  bottom  of  an  ordinary 
Hessian  or  clay  crucible.  Over  this  place  15  grammes  of  black- 
flux  substitute  mixed  with  I  gramme  of  borax-glass.  The 
black-flux  substitute  is  made  by  mixing  ten  parts  of  sodium 
bicarbonate  with  three  parts  of  flour.  On  top  of  the  charge  is 
placed  a  cover  of  salt,  and  on  this  several  lumps  of  charcoal. 
The  fusion  is  performed  in  the  wind-furnace,  using  a  coke  fire, 
or  in  the  muffle-furnace.  The  crucibles  should  be  left  in  the 
fire  for  front  one  hour  to  one  hour  and  twenty  minutes.  The 
fire  should  be  hot — between  a  bright  red  and  a  white  heat,  but 
not  as  hot  as  a  white  heat.  The  crucibles  are  removed  from 
the  furnace  and  allowed  to  cool.  When  cold  they  are  broken 
open  and  the  slag  removed  from  the  buttons,  which  are  then 
ready  for  weighing.  The  slag  should  be  clear  and  well  fused. 

This  method  requires  that  the  ore  should  be  quite  pure, 
and  should  contain  a  high  per  cent  of  tin.  If  the  ore  is  low- 
grade,  it  should  be  first  concentrated  by  washing  in  a  gold- 
pan  or  by  coarse  jigging.  In  this  case  the  sample  should 
be  weighed,  then  washed  until  most  of  the  silica,  iron,  etc., 
is  removed.  The  concentrates  are  now  dried  and  weighed. 
From  the  dry  concentrates  two  portions  of  5  grammes  each 
are  taken  for  assay. 

The  method  of  calculating  results  is  illustrated  by  the 
following  example : 

Sample  weighed 500  grammes. 

Concentrates  weighed 55         " 

Assay  of  5  grammes  concentrates  gave  tin 3.5      " 

tt  «     r  <<  «  (i  n  2  A.         C'' 


Average 3.45 

Hence =  37-95  gms-  tin  in  the  55  gms.  of  concen« 

,  37-95  X  100 
trates  ;  and  -  =  7.59  per  cent  tin  in  the  ore. 


CHAPTER   XIII. 
COPPER  (Cu). 

Two  wet  methods  for  the  determination  of  copper  in  ores 
and  furnace-products  are  generally  used  in  the  United  States, 
as  follows  :  The  volumetric  assay,  by  a  standard  solution  of 
potassium  cyanide,  and  the  battery-assay.  In  addition  to 
these,  the  colorimetric  method  and  the  volumetric  iodide 
method  are  sometimes  used. 

Volumetric  Assay  by  Means  of  Standard  Potassium- 
cyanide  Solution. — The  best  and  most  rapid  method  for 
making  this  assay  is  the  method  developed  by  Mr.  A.  H. 
Low,  late  chemist  to  the  Boston  and  Colorado  Smelting  Com- 
pany at  Argo,  Colorado.*  The  method  is  essentially  that  of 
Dr.  Steinbeck*,  but  so  modified  as  to  save  considerable  time, 
while  insuring  equal  if  not  greater  accuracy.  Treat  I  gramme 
of  the  pulverized  ore  in  a  flat-bottomed  flask  (250  cc.  capacity), 
or  casserole,  with  7  cc.  of  nitric  and  5  cc.  sulphuric  acid. 
Commercial  acids  will  answer  all  purposes.  Heat  till  the  nitric 
acid  is  all  expelled  and  the  sulphuric  acid  is  boiling  freely. 
Sulphur,  if  present,  is  usually  partially,  sometimes  entirely, 
volatilized,  a  portion  recondensing  on  the  neck  of  the  flask. 
What  is  in  the  bottom  of  the  flask  should  be  melted  into  glob- 
ules, which  are  yellow  when  cold  and  free  from  copper.  Allow 
the  flask  and  contents  to  cool  sufficiently,  and  add  6  grammes 
of  commercial  sheet  zincf  cut  into  small  strips  of  about  3 
grammes  each.  Shake  the  contents  of  the  flask  in  order  to 
break  up  any  cake  formed  in  the  bottom,  and  allow  to  stand 

*  Transactions  of  the  Colorado  Scientific  Society,  Vol.  I. 
f  Aluminum  may  be  substituted  for  zinc  with  advantage. 

'54 


COPPER.  1 5  5 

five  minutes.  Then  add  50  cc.  of  water  and  20  cc.  of  sulphuric 
acid  to  rapidly  dissolve  the  excess  of  zinc,  which  usually  takes 
about  five  minutes  more.  When  solution  of  the  zinc  is  com- 
plete, fill  up  to  the  neck  with  water,  allow  to  settle,  and  decant 
the  clear  supernatant  liquid.  This  may  be  tested  for  copper, 
if  desired,  with  sulphuretted-hydrogen  water,  bearing  in  mind 
that  antimony,  bismuth,  etc.,  may  be  present  and  give  dis- 
colorations  likely  to  be  mistaken  for  copper.  As  a  rule,  no 
discoloration  or  only  an  extremely  faint  one  will  be  observed, 
and  consequently  the  test  is  usually  omitted.  Fill  up  with 
water  and  decant  twice  more.  The  residue  in  the  flask  may 
consist  of  gangue  and  copper,  besides  various  other  constitu- 
ents of  the  ore  and  the  impure  reagents  used,  such  as  silver, 
gold,  lead,  arsenic,  antimony,  etc.,  of  which  only  silver  is  likely 
to  interfere  with  the  assay.  Now  add  5  cc.,  pretty  exactly 
measured,  of  pure  concentrated  nitric  acid,  and  boil,  to  expel 
the  red  fumes.  Now  add  a  single  drop  of  strong  hydrochloric 
acid,  and  if  much  silver  (i  per  cent  or  more)  is  thus  indicated, 
add  a  second  drop  of  hydrochloric  acid,  which  is  usually  quite 
sufficient,  and,  after  dilution  with  a  little  water,  filter.  A 
simple  cloudiness  or  very  slight  precipitate  of  silver  may  be 
disregarded.  To  the  somewhat  dilute  acid  solution  add  10  cc. 
of  strong  ammonia-water  and  cool. 

One  of  two  courses  is  now  to  be  chosen.  If  the  color  of 
the  solution  indicates  that  not  more  than  3  per  cent  of  copper 
is  present,  add  about  125  cc.  of  water  and  filter,  using  a  filter 
of  about  6  inches  in  diameter  and  folded  into  corrugations.  It 
filters  rapidly,  and  the  small  amount  of  dilute  solution  remain- 
ing in  the  pores  of  the  filter  generally  need  not  be  washed  out. 
If  a  larger  amount  of  copper  is  present,  the  125  cc.  of  water  is 
added  and  the  titration  with  potassium  cyanide  is  proceeded 
with,  until  all  but  about  2  or  3  per  cent  of  the  copper  has  been 
neutralized,  and  then  the  liquid  should  be  filtered  as  before. 
The  object  of  this  filtration  is  to  remove  the  gangue,  lead, 
ferric  hydrate,  etc.,  which  may  be  present,  and  afford  a  clear 
solution  with  which  to  complete  the  titration.  The  cyanide 
solution  is  run  into  the  filtered  liquid,  and  when  within  a  few 


156  A   MANUAL   OF  PRACTICAL  ASSAYING. 

cubic  centimetres  of  the  end  the  bulk  of  the  solution  should 
be  noted  and  distilled  water  added,  if  necessary,  so  that  the 
final  bulk  will  be  about  180  cc.  This  is  about  the  bulk  which 
should  be  attained,  without  any  dilution,  in  the  assay  of  a  sub- 
stance containing  about  80  per  cent  copper,  which  is  the  maxi- 
mum amount  considered  in  the  present  scheme,  starting  with 
one  gramme  of  substance.  The  final  addition  of  the  cyanide 
should  be  made  drop  by  drop,  the  flask  being  well  shaken  each 
time,  until  the  blue  or  lilac  tint  can  scarcely  be  discerned  at  the 
upper  edges  of  the  liquid  when  viewed  against  a  white  back- 
ground. Many  chemists  titrate  to  a  faint  rose  or  pink  tint. 
The  cyanide  solution  should  be  of  such  a  strength  that  I  cc. 
will  correspond  to  5  milligrammes  of  copper.  Accordingly,  it 
will  contain  from  55  to  60  grammes  of  commercial  cyanide  of 
potassium  to  the  litre.  It  should  be  kept  in  a  closed  bottle, 
preferably  of  dark-green  glass,  covered  with  black  paper,  and 
be  protected  with  a  layer  of  coal-oil.  To  standardize,  dissolve 
from  three  to  five  tenths  of  a  gramme  of  pure  copper-foil  in  5 
cc.  of  pure  concentrated  nitric  acid  ;  boil  off  red  fumes,  dilute 
slightly,  add  10  cc.  of  strong  ammonia-water,  cool,  and  titrate. 
When  near  the  end  add  distilled  water,  to  bring  the  final  bulk 
up  to  about  1 80  cc.,  and  finish  as  described  above. 

Although  most  ores  yield  to  the  above  treatment  with 
nitric  and  sulphuric  acid,  the  addition  of  a  little  hydrochloric 
acid  is  sometimes  necessary  and  advantageous.  When  the 
amount  of  silver  present  is  known,  it  need  not  be  removed, 
but  a  correction  can  be  applied  to  the  final  result  instead. 
2Ag  =  Cu,  or  i  per  cent  Ag  —  0.3  per  cent  Cu,  about. 

When  large  amounts  of  arsenic,  etc.,  are  present,  they  may 
be  only  partially  precipitated  by  the  treatment  with  zinc,  and 
may  consequently,  when  the  zinc  is  dissolved,  react  on  the  pre- 
cipitated copper  and  cause  the  solution  of  a  small  portion. 
With  such  ores  more  time  should  be  allowed  for  the  zinc  to  act 
before  dissolving  the  excess,  and  also  the  first  decantation 
should  be  made  as  soon  as  possible  after  the  zinc  has  all  been 
dissolved.  An  accurate  assay  can  be  made  by  this  method  in 
from  20  to  30  minutes. 


COPPER.  157 

Battery-assay. — The  amount  of  ore  or  substance  to  be 
taken  will  depend  on  the  amount  of  copper  which  it  contains. 
For  the  assays  of  a  substance  containing  $  per  cent  or  less  of 
copper  3  grammes  should  be  taken,  while  for  a  substance  con- 
taining over  60  per  cent  of  copper  0.25  of  a  gramme  will  be 
sufficient.  The  usual  amount  is  I  gramme,  but  the  assayer 
should  use  his  judgment  according  to  the  amount  of  copper  he 
thinks  the  substance  contains. 

The  substance  is  dissolved  in  the  same  manner  described 
under  the  head  of  the  cyanide-assay.  It  is  then  diluted  with 
a  little  distilled  water  and  in  order  to  remove  silver,  if  present, 
one  or  two  drops  of  hydrochloric  acid  (in  extreme  cases  the 
amount  necessary  may  be  larger,  but  care  should  always  be 
exercised  to  avoid  an  excess,  as  this  interferes  with  the  results) 
are  added,  and  the  liquid  filtered  into  a  platinum  dish  of  about 
60  to  70  cc.  capacity.  This  dish  is  best  made  of  the  lightest 
platinum  which  will  admit  of  ordinarily  careful  handling  when 
filled  with  the  solution.  The  platinum  dish  is  then  placed  on 
a  piece  of  copper  or  brass,  connected  with  the  negative  or  zinc 
element  of  the  battery  (a  very  good  battery  for  this  purpose  is 
the  ordinary  Bunsen  cell),  while  the  liquid  in  the  dish  is  con- 
nected with  the  positive  pole  either  by  a  platinum  wire  attached 
to  the  positive  pole  and  coiled  in  a  horizontal  spiral,  or  by  a 
copper  wire  on  which  is  hung  a  strip  of  platinum-foil  the  ends 
of  which  are  immersed  in  the  liquid.  About  8  hours  is  the 
time  usually  required  to  complete  the  assay,  the  time  of  course 
depending  on  the  amount  of  copper  present  and  the  activity  of 
the  electrical  action.  In  order  to  determine  if  all  the  copper 
has  been  precipitated,  a  drop  of  the  solution  is  removed  from 
the  dish  by  means  of  a  pipette  and  tested  with  sulphuretted- 
hydrogen  water. 

If  this  test  shows  all  the  copper  to  have  been  precipitated, 
the  liquid  is  best  removed  from  the  dish  by  siphoning  off  by 
means  of  a  bent-glass  tube,  the  solution  being  replaced  by  dis- 
tilled water  as  fast  as  it  siphons  off,  until  it  is  washed  suffi- 
ciently. When  washed  sufficiently  the  wires  are  removed  and 
the  dish  is  washed  with  alcohol,  which  is  poured  off  and  the 


158  A    MANUAL    OF  PRACTICAL   ASSAYING. 

contents  dried  by  setting  fire  to  the  alcohol,  which  adheres  to 
the  sides,  after  which  the  dish  with  its  brilliant  coating  of  rose- 
red  copper  is  weighed.  The  difference  between  the  weight  of 
the  dish  and  its  weight  after  the  precipitation  of  the  copper 
upon  it  represents  the  weight  of  copper  precipitated,  from 
which  the  percentage  of  copper  can  be  calculated.  The  pre- 
cipitated copper  should  always  be  of  a  rose-red  color,  otherwise 
/the  result  .cannot  be  relied  upon.  Many  of  the  different  ele- 
ments, if  in  solution,  will  be  liable  to  be  precipitated  together 
with  the  copper,  and  will  affect  the  result,  sometimes  to  a  very 
.great  extent.  Messrs.  Torrey  and  Eaton  of  New  York*  have 
made  a  large  number  of  tests  with  the  cyanide  and  battery 
methods,  and  the  results  of  their  tests  and  the  conclusions  which 
they  draw  from  them  are  that  in  all  cases  the  cyanide  method 
is  more  reliable  than  the  battery  method.  When  much  arsenic, 
antimony,  bismuth,  etc.,  are  present,  a  very  good  method  of 
procedure  is  to  treat  the  ore  according  to  the  method  described 
under  the  head  of  cyanide-assay,  and  after  dissolving  the  pre- 
cipitated copper  with  nitric  acid,  add  sulphuric  acid  and  evap- 
orate to  expel  the  nitric  acid,  filter  if  necessary,  and  proceed  to 
precipitate*the  copper  by  the  battery.  This  method  is  prefer- 
able to  the  method  described  by  Cairns,t  and  some  other 
authors,  of  precipitating  the  metals  of  groups  VI  and  VII  by 
means  of  sulphuretted  hydrogen  and  then  dissolving  the  sul- 
phides of  arsenic,  antimony,  and  tin  by  the  addition  of  caustic 
potash,  on  account  of  its  greater  speed  and  the  less  liability  of 
loss  of  copper  in  manipulation.  The  use  of  sulphuretted  hy- 
drogen is  not  only  a  source  of  annoyance  and  discomfort  to  the 
chemist,  but,  without  very  careful  manipulation,  introduces  a 
liability  of  error  owing  to  the  difficulty  of  handling  and  wash- 
ing the  precipitate. 

Taking  all  of  the  liabilities  of  error  into  consideration,  the 
writer  agrees  with  Messrs.  Torrey  and  Eaton  that  the  cyanide 
method  is  generally  more  accurate  and  preferable  to  the  battery 
method. 

*  See  Engineering  and  Mining  Journal  for  May  and  June  1885. 
f  See  Cairns'  Quantitative  Analysis 


COPPER.  159 

A  very  ingenious  and  simple  apparatus  for  the  estimation 
of  copper  by  electrolytic  deposition  has  been  devised  by  Mr. 
A.  H.  Low  of  Denver,  Colo.,*  and  is  for  sale  by  Eimer  & 
Amend  of  New  York.  This  apparatus  not  only  shortens  the 
time  required  for  the  determination  of  the  copper,  but  consid- 
erably lessens  the  expense  of  apparatus,  requiring  no  expensive 
batteries  and  platinum  dishes.  It  is  consequently  to  be  highly 
recommended  for  use  in  a  laboratory  where  a  large  number  of 
determinations  are  required  to  be  made  daily  by  means  of 
electrolytic  deposition.  This  method  fails  when  a  large  quan- 
tity of  ferric  sulphate  is  contained  in  the  solution. 

Colorimetric  Method. —  This  method  is  to  be  recom- 
mended for  the  estimation  of  copper  in  substances  containing 
less  than  2  per  cent,  as,  for  example,  in  slags  from  copper- 
smelting  operations  and  in  tailings  from  concentrating-works. 
The  method  was  first  suggested  by  Heine.f  The  method  given 
here  is  a  modification  of  Heine's  method.  Where  the  amount 
of  iron  and  alumina  present  is  small,  previous  precipitation  of 
the  copper  is  not  necessary,  but  in  the  case  of  slags  and  tail- 
ings, for  which  this  method  is  particularly  adapted,  it  would  be 
impossible  to  wash  out  all  of  the  copper  salts  with  the  small 
amount  of  wash-water  which  can  be  used;  hence  in  this  case 
previous  precipitation  of  the  copper  is  necessary. 

The  method  consists  essentially  in  converting  the  copper  in 
the  substance  to  be  tested  into  ammonium  cupric  nitrate,  and 
comparing  the  blue  color  produced  with  that  produced  by 
dissolving  a  known  amount  of  copper  in  the  same  amount 
of  acid  and  using  the  same  amount  of  ammonia  as  is  used  in 
the  regular  assay.  With  each  set  of  assays  a  separate  stand- 
ard should  be  run,  as  the  blue  color  is  not  constant,  but  fades. 
For  the  standard  either  an  accurately  weighed  amount  of  pure 
copper  can  be  taken,  or  the  same  amount  of  slag  or  tails 
as  is  used  in  the  regular  assay  may  be  taken.  Where  the 
latter  method  is  adopted,  and  it  is  generally  preferable,  as  there 


*  Proceedings  of  the  Colorado  Scientific  Society,  Vol.  I. 

f  See  Mitchell  on  Practical  Assaying;  Kerl's  Metallurgy  of  Copper. 


l6o  A    MANUAL    OF  PRACTICAL   ASSAYING. 

is  less  liability  to  error  in  weighing  than  where  a  small  amount 
of  pure  copper  is  taken,  and  it  also  introduces  the  same  con- 
ditions into  the  standard  as  are  present  in  the  regular  assay,  of 
course  the  copper  must  have  been  previously  accurately  deter- 
mined in  the  sample  from  which  the  standard  is  weighed  out. 
A  few  ounces  of  the  material  will  last  for  a  large  number  of 
assays.  In  order  to  make  the  assay,  the  amount  of  material 
for  assay  and  of  the  standard  are  weighed  out  and  treated  in 
the  same  manner  as  described  under  the  head  of  the  cyanide- 
assay.  When  the  precipitated  copper  has  been  thoroughly 
washed  by  decantation  it  is  dissolved  in  a  small  amount  of 
nitric  acid  (about  2  cubic  centimetres  is  sufficient),  and  an  excess 
of  strong  ammonia  added  (about  4  cubic  centimetres),  the  acid 
and  ammonia  being  pretty  accurately  measured.  The  solution 
after  slight  dilution  with  water  is  then  filtered  into  a  graduated 
tube  for  comparison,  and  washed.  Two  of  these  graduated 
tubes  are  necessary, — one  for  the  regular  assay  and  one  for  the 
standard.  They  should  be  of  thin  colorless  glass  and  of  the 
same  internal  arid  external  diameter,  and  should  also  be  pro- 
vided with  a  stopper,  so  that  the  solution  may  be  thoroughly 
mixed  by  shaking.  The  assayer  can  prepare  and  graduate  these 
tubes  for  his  own  use. 

The  method  of  determining  the  percentage  of  copper  pres- 
ent is  best  illustrated  by  an  example  :  Suppose  the  material 
used  for  making  the  standard  assay  contained  exactly  I  per  cent 
of  copper ;  then  if  a  half  gramme  was  taken,  and  after  filtering 
into  the  tube  and  washing,  the  contents  of  the  tube  were 
diluted  up  to  the  25-cc.  mark  with  distilled  water,  each  cc.  of 
the  solution  would  contain  -fa  milligramme  of  copper,  or  0.2 
milligramme.  The  regular  assay  is  then  run,  and  after  filter- 
ing into  the  tube  the  color  of  the  solution  is  noted,  and  it  is 
diluted  with  distilled  water,  shaking  after  each  addition  of 
water  until  the  tint  or  color  in  the  two  tubes  is  the  same  when 
compared  together  against  a  white  background.  The  height 
of  the  liquid  in  the  tube  is  then  noted.  Suppose  it  reads  22  cc. 
Now,  as  each  cubic  centimetre  of  the  standard  solution  contains 
0.2  milligramme  of  copper,  each  cubic  centimetre  of  the  solu- 


COPPER.  l6l 

tion  in  the  other  tube  contains  the  same  amount;  hence 
22  X  0.2  =  4.4  milligrammes. 

500  mgs.  ore  taken  :  4.4  mgs.  Cu  =  100:  x\  x  =  o.88$Cu. 

Volumetric  Iodide  Method. — This  method,  as  modified 
by  A.  H.  Low,*  is  at  present  largely  used  in  the  West  for 
the  technical  estimation  of  copper,  and  in  the  opinion  of  the 
author  is  one  of  the  most  accurate  methods  which  we  have. 

Prepare  a  solution  of  sodium  hyposulphite  containing 
19.59  grammes  of  the  pure  salt  to  the  litre.  Standardize  as 
follows:  Weigh  out  0.2  gramme  of  pure  copper-foil,  place  in 
a.  flask  of  about  250  cc.  capacity,  add  5  cc.  of  a  mixture  of 
-equal  volumes  of  concentrated  nitric  acid  and  water,  and 
thoroughly  boil  off  the  red  fumes.  Remove  from  the  lamp 
and  add  20  cc.  of  a  cold  saturated  solution  of  zinc  acetate. 
Heat  to  boiling,  cool  to  the  ordinary  temperature,  and  dilute 
with  water  to  about  50  cc.  Add  3  grammes  of  potassium 
iodide,  and  shake  the  solution  gently  until  the  salt  dissolves. 
The  following  reaction  takes  place : 

Cu(C2H802)2  +  2KI  =  Cul  +  2KC2H802  +  I. 

The  free  iodine  imparts  a  brown  color  to  the  solution. 
Titrate  the  solution  immediately  with  the  hyposulphite  solu- 
tion until  the  brown  color  is  nearly  destroyed,  add  a  few  drops 
of  starch  solution,  and  continue  the  titration  until  the  blue 
•color  disappears.  When  near  the  end  allow  a  little  time  after 
the  addition  of  each  drop  to  avoid  passing  the  end  point. 
This  titration  should  show  each  cc.  of  the  hyposulphite  solu- 
tion to  correspond  to  about  0.005  gramme  of  copper;  hence, 
in  the  assay  of  ores,  etc.,  if  0.5  gramme  of  material  is  taken, 
each  cc.  of  the  hyposulphite  will  be  equivalent  to  about  I  per 
cent  of  copper. 

The  starch  solution  is  prepared  by  boiling  0.5  of  starch 
with  water,  diluting  to  250  cc.  with  hot  water  and  filtering. 
It  should  be  used  cold,  and  must  be  prepared  frequently,  as 
it  does  not  keep  well.  The  hyposulphite  solution  is  quite 
stable,  but  should  be  restandardized  from  time  to  time. 

For  the  assay  of  ores  and  mattes,  treat  0.5  gramme  in  a 

*  Journal  of  the  American  Chemical  Society,  1896.     Engineering  and 
Mining  Journal,  May  23.  1896. 


1 62  A    MANUAL    OF  PRACTICAL   ASSAYING. 

flask  of  250  cc.  capacity  with  6  cc.  of  strong  nitric  acid,  and 
evaporate  nearly  to  dryness.  Add  5  cc.  of  strong  hydro- 
chloric acid,  boil,  and  as  soon  as  complete  solution  is  effected, 
add  5  cc.  of  strong  sulphuric  acid.  Heat  strongly,  best  by 
manipulating  the  flask  in  a  holder  over  a  small  naked  flame, 
until  the  more  volatile  acids  are  expelled  and  sulphuric  fumes 
are  evolved  freely.  Cool,  add  20  cc.  of  cold  water,  and  heat 
to  boiling  to  effect  complete  solution.  Filter  into  a  small 
beaker,  wash  with  hot  water,  and  endeavor  to  keep  the  volume 
of  the  filtrate  down  to  50  or  60  cc.  Place  in  the  beaker  two- 
pieces  of  aluminium  about  one  and  a  half  inches  square,  one 
sixteenth  of  an  inch  thick,  with  the  four  corners  bent  for  one- 
fourth  inch,  alternately  up  and  down,  at  right  angles.  Add  5 
cc.  of  strong  sulphuric  acid,  cover  the  beaker,  and  boil  for 
seven  minutes.  Unless  the  bulk  of  the  solution  is  excessive, 
this  will  generally  be  sufficient  to  precipitate  all  the  copper. 
Transfer  the  solution  back  to  the  original  flask,  rinsing  in  with 
hot  water  as  much  of  the  copper  as  possible.  Allow  the 
copper  in  the  flask  to  settle,  and  decant  the  liquid  through  a 
filter.  Wash  the  copper  two  or  three  times,  retaining  it  as. 
completely  as  possible  in  the  flask.  Pour  upon  the  aluminium 
in  the  beaker  5  cc.  of  a  mixture  of  equal  volumes  of  strong 
nitric  acid  and  water,  warm  gently  until  the  copper  is  dissolved, 
and  pour  the  solution  through  the  filter,  receiving  the  filtrate 
in  the  flask  containing  the  main  portion  of  the  copper.  Heat 
the  contents  of  the  flask  to  dissolve  the  copper,  add  0.5 
gramme  of  potassium  chlorate,  and  boil  to  insure  the  oxidation 
of  any  arsenic  present  to  arsenic  acid.  Place  the  flask  under 
the  funnel,  wash  the  beaker,  filter  thoroughly  with  hot  water, 
and  boil  the  contents  of  the  flask  to  remove  every  trace  of 
red  fumes.  All  the  copper  is  now  in  the  flask  as  nitrate. 
Add  the  zinc  acetate,  and  proceed  from  this  point  precisely 
as  described  with  the  original  nitrate  of  copper  solution  in  the 
standardization  of  the  hyposulphite,  finally  calculating  the 
percentage  of  copper  present  from  the  amount  of  standard 
hyposulphite  used. 

Silver,  lead,  and  bismuth  do  not  interfere,  except  that  the 
latter  is  liable  to  mask  the  end-point  before  adding  the  starch. 


CHAPTER   XIV. 
BISMUTH  (Bi). 

ABOUT  the  only  determinations  of  bismuth  which  the  metal- 
lurgical  chemist  will  be  called  on  for  are  in  refined  lead,  base 
bullion,  and  occasionally  ores.  The  methods  given  are  ab- 
stracted from  a  paper  by  L.  G.  Eakins.* 

Refined  Lead. — After  rolling  into  thin  sheets  the  lead  is 
cut  up  into  small  pieces,  75  gms.  of  which  are  introduced  into 
a  beaker,  and  90  cc.  of  nitric  acid  (1.42  sp.  gr.)  and  400  cc.  of 
water  are  added.  The  solution  is  heated,  replacing  the  evap- 
orated water,  and  as  soon  as  everything  is  dissolved  the  solu- 
tion is  transferred  to  an  810  cc.  graduated  flask  containing  30  cc. 
of  strong  sulphuric  acid  somewhat  diluted.  The  flask  is  filled 
to  the  mark,  stoppered,  and  well  shaken.  After  allowing  the 
precipitate  to  subside  somewhat,  the  solution  is  filtered  through 
a  dry  rapid  filter  into  a  529  cc.  flask,  which  is  filled  exactly  to 
the  mark.  The  whole  operation  is  performed  so  rapidly  that 
the  change  in  volume  due  to  cooling  can  be  neglected.  The 
following  calculation  shows  the  amount  of  material  the  529  cc. 
of  solution  represents : 

Volume  of  liquid  and  precipitate 810.00   cc. 

Volume  of  lead  sulphate  from  75  gms.  of  lead     16.875  cc. 

Actual  volume  of  liquid 793.125  cc. 

Then 

793.125  :  529  : :  75  :  x(x  =  50.02  gms.), 

or  in  round  numbers  50  gms.  of  the  lead. 

The  solution  is  evaporated  in  a  large  beaker,  and  when 
sufficiently  concentrated  is  transferred  to  a  porcelain  casserole 

*  Proceedings  of  the  Colorado  Scientific  Society,  Feb.  1895. 

163 


164  A   MANUAL    OF  PRACTICAL  ASSAYING. 

and  evaporated  until  SO3  fumes  are  freely  evolved.  After 
cooling  it  is  diluted  with  cold  water  to  125  cc.,  and  boiled 
briskly  for  a  few  minutes  to  insure  re-solution  of  all  the  bismuth 
sulphate. 

After  cooling,  filter,  washing  the  precipitated  lead  sulphate 
with  dilute  sulphuric-acid  water.  Warm  the  filtrate  and  pass 
sulphuretted  hydrogen  gas  for  lOto  15  minutes;  allow  to  stand 
warm  until  sulphides  have  settled,  filter,  and  wash  with  hot 
water.  Return  the  precipitate  to  the  beaker  in  which  the  pre- 
cipitation took  place,  and  add  15  to  20  cc.  of  yellow  potassium 
sulphide.  Heat  to  boiling,  dilute,  and  decant  through  the  same 
filter  as  used  for  filtration  of  the  sulphides ;  repeat  treatment 
with  fresh  alkaline  sulphide  ;  finally  transfer  the  precipitate  to 
the  filter,  and  wash  with  water  containing  some  of  the  alkaline 
sulphide.  Place  the  filter  and  precipitate  in  the  same  beaker, 
add  5  cc.  of  strong  nitric  acid  diluted  to  25  cc.,  warm  to  effect 
solution,  and  filter  into  a  porcelain  dish ;  burn  papers  at  a  low 
heat,  adding  the  ash  to  the  solution ;  add  3  cc.  of  strong  sul- 
phuric acid,  and  evaporate  to  fumes  of  SO3.  Cool,  dilute,  boil, 
allow  to  cool,  filter,  and  wash  with  dilute  sulphuric  acid.  To 
the  filtrate  add  solution  of  sodium  carbonate  until  the  solution 
is  slightly  alkaline  (a  drop  of  methyl  orange  is  a  good  indicator), 
and  add  a  few  drops  of  a  strong  solution  of  potassium  cyanide. 
Boil  for  a  few  minutes,  allow  to  stand  warm  until  the  precipi- 
tate has  settled  and  the  supernatant  liquid  is  clear.  Filter 
through  a  quite  close  paper,  washing  with  warm  water  ;  dissolve 
the  precipitate  in  warm  dilute  nitric  acid ;  add  ammonia  to 
alkalinity,  and  3  to  5  cc.  of  ammonium-carbonate  solution. 
Heat  to  boiling,  and  allow  to  stand  warm  until  the  bismuth  car- 
bonate has  settled ;  filter,  and  wash.  Dry  filter  and  precipi- 
tate, remove  the  latter  as  completely  as  possible,  burn  filter  and 
add  its  ash  to  precipitate,  ignite  in  a  small  porcelain  crucible  at 
a  low  red  heat,  and  weigh  as  Bi2O3. 

Lead  Bullion. — Treat  as  above  until  measured  portion  of 
clear  solution  is  obtained.  The  solution  is  now  rendered 
ammoniacal,  50  cc.  excess  of  ammonia  is  added,  and  hydrogen 
sulphide  is  passed  nearly  to  saturation  when  20  cc.  more  of 


BISMUTH.  165 

ammonia  is  added,  and  the  whole  is  allowed  to  stand  warm 
until  the  precipitate  has  completely  settled.  Filter  and  wash 
slightly;  place  filter  and  precipitate  in  a  beaker,  add  15  cc.  of 
strong  nitric  acid,  dilute  to  60  cc.,  warm  until  sulphides  are 
decomposed,  and  filter  into  a  porcelain  dish.  Burn  filter  and 
add  its  ash  to  dish,  then  10  cc.  of  strong  sulphuric  acid,  and 
evaporate  to  fumes  of  SO3.  From  this  point  on  the  determina- 
tion is  as  with  refined  lead,  except  that  a  larger  quantity  of  the 
alkaline  sulphides  are  required.  At  the  second  evaporation  the 
sulphuric  acid  used  should  be  increased  to  6  cc.  When  pre- 
cipitating with  sodium  carbonate  and  potassium  cyanide  enough 
of  the  latter  must  be  added  to  bring  all  of  the  silver,  copper, 
and  cadmium  into  solution. 

Ores. — For  the  estimation  of  bismuth  in  lead  ores  the  fol- 
lowing will  answer:  Make  a  number  of  fusions  as  in  the  fire- 
assay  for  lead  (see  page  137),  combine  the  buttons,  and  treat 
exactly  as  in  the  assay  of  base  bullion  for  bismuth. 

For  ores  other  than  lead  ores  add  to  each  charge  about  one 
fifth  of  the  weight  of  ore  taken  of  some  bismuth-free  lead  salt, 
as  carbonate,  fuse,  and  proceed  with  the  lead  buttons  as  in  the 
case  of  lead  bullion. 

Whilst  this  method  is  not  strictly  accurate,  it  will  answer 
for  all  technical  purposes. 


CHAPTER   XV. 

CADMIUM  (Cd). 

CADMIUM  may  be  determined  gravimetrically  by  precipi- 
tation as  CdCO9,  ignition  to  CdO,  and  weighing  as  such,  or  it 
may  be  determined  volumetrically  by  means  of  a  standard 
solution  of  potassium  ferrocyanide. 

There  are  several  other  methods,  both  gravimetric  and 
volumetric,  for  which  see  Fresenius,  Rose,  etc. 

Gravimetric  Determination. — Decompose  the  ore  with 
nitrohydrochloric  acid,  evaporate  nearly  to  dryness  to  drive 
off  the  nitric  acid,  leaving  but  a  small  quantity  of  free  hydro- 
chloric acid  present.  Dilute  with  warm  water,  filter,  and  wash 
thoroughly  with  hot  water.  Through  the  filtrate  pass  a 
rapid  current  of  sulphuretted  hydrogen  until  all  members  of 
the  sulphuretted-hydrogen  group  are  completely  precipitated. 
The  solution  should  not  contain  a  large  excess  of  hydrochloric 
acid ;  if  it  does  the  cadmium  will  fail  to  precipitate.  Filter 
off  the  precipitated  sulphides,  and  wash  with  sulphuretted- 
hydrogen  water.  Dissolve  the  precipitated  sulphides  in  hot 
hydrochloric  acid,  and  boil.  If  lead  is  present  some  will  pass 
into  solution,  and  can  be  removed  by  precipitation  with  sul- 
phuric acid.  Filter  and  wash.  The  filtrate  will  contain  the 
cadmium  as  a  chloride.  Precipitate  the  cadmium  with  a  slight 
excess  of  potassium  carbonate  (pure),  filter,  and  wash  precipi- 
tate thoroughly  with  warm  water.  Dry  the  precipitate,  and 
when  dry  remove  carefully  from  the  filter-paper,  introducing 
it  into  a  weighed  crucible.  Moisten  the  filter-paper  with  a 
strong  solution  of  ammonium  nitrate,  wrap  it  in  a  spiral  of 
platinum  wire,  and  ignite  over  an  alcohol  flame,  allowing  the 
ash  to  fall  into  the  crucible.  The  cadmium  carbonate  adhering 
to  the  filter-paper  is  liable  to  be  reduced  by  the  carbon  of 
the  filter,  and  volatilized  ;  hence  the  addition  of  ammonium 
nitrate,  and  the  care  required  in  ignition.  Transfer  all  the  ash 

1 66 


CADMIUM.  167 

to  the  crucible,  and  ignite  to  constant  weight.  Care  should 
be  exercised  during  ignition  that  the  cadmium  oxide  is  not 
reduced.  If  reduced  some  will  be  volatilized  and  lost.  Weigh 
the  cadmium  oxide,  and  calculate  the  percentage  of  cadmium. 

The  results  are  liable  to  be  a  little  low. 

Volumetric  Determination. — This  requires  a  standard 
solution  of  potassium  ferrocyanide  of  about  two-thirds  the 
strength  of  the  solution  used  for  the  determination  of  zinc. 
If  its  standard  for  zinc  is  known  its  standard  for  cadmium  may 
be  calculated  as  follows :  Let  a  =  mgs.  of  zinc  which  I  cc.  of 
ferrocyanide  solution  is  equivalent  to,  and  x  =  mgs.  of  cadmium 
which  i  cc.  of  the  solution  should  precipitate ;  then 

I3o(mol.  wt.  2Zn)  :  224 (mol.  wt.  2Cd)  : :  a  :  x. 

It  is  best  to  standardize  the  solution  with  a  solution  of 
cadmium  known  to  contain  a  certain  weight  of  cadmium. 

The  titration  is  performed  in  the  same  manner  as  in  the 
determination  of  zinc,  using  uranium  acetate  as  an  indicator. 
The  solution  should  not  contain  a  large  excess  of  hydrochloric 
acid,  as  cadmium  ferrocyanide  is  soluble  in  hydrochloric  acid. 
The  analysis  is  performed  as  follows:  Treat  I  gramme  of  ore 
in  the  same  manner  as  in  the  determination  of  zinc  (see  Chap- 
ter XXI),  and  filter  off  the  precipitated  oxides.  Neutralize 
the  filtrate  with  hydrochloric  acid,  and  add  a  slight  excess  of 
acid.  Dilute  with  warm  water,  and  pass  a  rapid  current  of 
sulphuretted  hydrogen.  Filter  off  the  precipitated  sulphides, 
wash  with  sulphuretted-hydrogen  water,  and  dissolve  the  pre- 
cipitate in  dilute  hot  hydrochloric  acid.  Dilute,  and  if  copper 
is  present  precipitate  it  with  test-lead  or  aluminium-foil.  The 
solution  is  now  ready  for  titration  with  the  standard  solution 
of  potassium  ferrocyanide. 

The  filtrate  from  the  precipitated  sulphides  may  be  used 
for  the  determination  of  zinc,  and  the  copper  (if  precipitated 
on  aluminium-foil)  may  be  determined  as  described  in  Chapter 
XIII. 

The  method  is  rapid,  and  gives  results  which  answer  all 
requirements  for  technical  purposes. 


•CHAPTER  XVI. 
IRON  (Fe). 

WHILST  many  different  methods  have  been  proposed  for 
the  determination  of  iron,  the  three  following  are  the  only  ones 
in  general  use  in  the  United  States  : 

1.  By  precipitation  with  ammonia,  filtration  and  ignition  to 
ferric  oxide,  weighing  as  such  ; 

2.  Volumetrically,  by  means  of  a  standard  solution  of  po- 
tassium permanganate  (Marguerite's  method)  ; 

3.  Volumetrically  by  means  of  a  standard  solution  of  po- 
tassium bichromate  (Peeny's  method). 

The  chemist  may  have  occasion  to  use  all  of  these 
methods,  as  one  very  frequently  gives  good  results  where  the 
others  fail.  Sometimes  a  combination  of  the  first  and  second 
or  first  and  third  may  be  employed  to  advantage.  When  the 
iron  is  to  be  determined  by  the  first  method  the  solution  from 
which  the  iron  is  precipitated  should  first  be  freed  from 
alumina,  chromium,  manganese,  titanium,  lead,  arsenic,  etc., 
which  are  wholly  or  in  part  precipitated  together  with  the 
ferric  hydrate.  As  this  is  not  always  possible,  especially  in 
technical  determinations,  a  combination  of  this  method  with 
one  of  the  volumetric  methods  may  be  employed  as  follows : 
The  iron,  either  in  a  hydrochloric-  or  sulphuric-acid  solution 
(sometimes  it  may  be  an  acetic-acid  solution  when  a  basic- 
acetate  precipitation  has  been  made  a$  described  under  the 
head  of  Alumina),  is  precipitated  by  adding  ammonia  in 
excess  to  the  warm  solution  and  the  solution  brought  to  a 
boil.  It  is  then  filtered  through  a  ribbed  filter-paper  and 
washed-  As  this  precipitate  is  exceedingly  bulky  and  difficult 

168 


IRON.  1 6^ 

to  wash,  a  filter-pump  may  here  be  used  to  advantage.  It 
should  be  washed  with  warm  water  until  the  washings  show 
only  a  faint  trace  of  chlorides  or  sulphates,  as  the  case  may  be. 
It  is  then  dissolved  on  the  filter-paper  directly  into  a  flask 
with  warm  diluted  hydrochloric  or  sulphuric  acids.  It  may 
then  be  reduced  and  determined  volumetrically  by  either  the 
second  or  third  methods,  as  the  case  may  be.  If  dissolved 
'with  sulphuric  acid,  it  may  be  determined  by  either  of  these 
methods ;  if  dissolved  by  hydrochloric  acid,  preferably  by  the 
bichromate  method. 

The  second  method  depends  upon  the  fact  that  when  a  so- 
lution of  potassium  permanganate,  which  has  an  intense  color,, 
is  dropped  into  a  solution  of  ferrous  oxide  it  gives  up  a  por- 
tion of  its  oxygen,  being  decomposed  into  salts  of  manganese 
and  potassium,  until  the  ferrous  oxide  is  completely  converted 
into  ferric  oxide.  The  moment  this  conversion  is  complete 
the  permanganate  imparts  a  pink  color  to  the  solution.  The 
reaction  which  takes  place  is  as  follows : 

ioFeS04  +  8H2S04  +  K2Mn2O8  = 

5Fe,(S04)3  +  2MnS04  +  K2SO4  +  8H2O. 

From  this  it  will  be  seen  that  in  order  to  determine  the 
amount  of  iron  in  solution  it  will  only  be  necessary  to  know 
what  amount  of  iron  one  cubic  centimetre  of  the  perman- 
ganate solution  will  oxidize  from  the  ferrous  to  the  ferric 
form. 

A  normal  solution  of  permanganate  is  a  solution  of  which 
i  cubic  centimetre  is  equal  to  or  converts  10  milligrammes 
of  iron  from  the  ferrous  to  the  ferric  state.  To  prepare  such 
a  solution,  dissolve  12  grammes  of  pure  crystallized  potassium 
permanganate  in  2030  cc.  of  distilled  water.  The  amount  of 
water  will  vary  slightly  with  different  permanganates,  so  that 
the  chemist  will  have  to  determine  for  himself  the  exact  amount 
with  each  new  bottle  of  permanganate  he  uses.  This  solution 
should  be  placed  in  a  stoppered  bottle  and  shaken  from  time 
to  time  until  ready  for  use.  It  is  best  to  make  up  the  solutioa 


170  A    MANUAL    OF  PRACTICAL  ASSAYING. 

at  least  forty-eight  hours  before  standardizing.  This  solution 
may  be  standardized  in  two  ways  : 

1st.  By  means  of  metallic  iron. 

The  iron  employed  for  the  purpose  is  usually  fine  piano- 
forte wire,  which  contains  99,7  per  cent  iron-.  This  should  be 
rubbed  with  sand-paper  until  bright,  in  order  to  remove  dust 
and  shellac,  with  which  it  is  sometimes  covered,  etc.,  before 
weighing  out.  It  is  best  to  weigh  it  out  on  the  button-bal- 
ance, two  portions  being  taken  of  about  150  and  200  milli- 
grammes, respectively.  These  portions  are  each  introduced 
into  a  flat-bottomed  flask  (250  cc.)  and  dissolved  with  dilute 
sulphuric  acid  by  gently  warming.  Many  chemists  (see  Fre- 
senius,  Cairns,  etc.)  use  a  valve-flask  for  this  purpose,  to  pre- 
vent the  oxidation  of  the  iron  during  solution.  The  writer 
prefers  to  dissolve  without  going  to  the  trouble  of  preparing  a 
valve-flask,  and  afterwards  reduce  the  small  amount  of  iron 
Avhich  may  have  been  oxidized,  by  the  addition  of  some  pure 
granulated  zinc.  This  reduction  takes  but  a  few  minutes. 
When  the  iron  is  all  reduced,  which  may  be  determined  by 
removing  a  drop  of  the  solution  on  a  glass  rod  and  testing  it 
on  a  porcelain  plate  with  a  drop  of  ammonium-sulphocyanate 
solution  (if  the  iron  is  all  reduced  to  the  proto  state  the  drop 
will  remain  colorless,  whilst  if  any  ferric  oxide  is  present  the 
drop  will  turn  red,  the  depth  of  the  color  depending  on  the 
amount  of  ferric  iron  present),  the  contents  of  the  flask  are 
diluted,  by  the  addition  of  cold  distilled  water,  and  the  solu- 
tion decanted  off  from  the  zinc  into  a  large  beaker,  or  prefer- 
ably an  ordinary  glass  battery-jar,  the  jar  being  much  less 
liable  to  breakage  in  subsequent  stirring  of  the  solution.  The 
flask  and  zinc  are  well  washed,  the  washings  being  transferred 
to  the  jar.  The  solution  is  then  diluted  up  to  about  700  cc. 
(it  is  a  good  plan  to  scratch  a  mark  on  the  side  of  the  jar  at 
this  point),  and  about  20  cc.  of  dilute  sulphuric  acid  are  added. 
In  making  subsequent  determinations  it  is  better  to  use  the 
same  or  a  similar  jar,  and  always  fill  to  the  same  point  so  as 
to  have  the  same  bulk  of  solution.  Sometimes  minute  par- 
ticles of  zinc  will  be  decanted  over  with  the  washings,  but 


IRON.  171 

these  will  quickly  be  dissolved  by  the  excess  of  sulphuric  acid. 
As  soon  as  all  effervescence  of  gas  has  ceased, — the  solution 
should  not  be  allowed  to  stand  too  long,  as  some  iron  is  liable 
to  be  oxidized  by  contact  with  the  air, — the  solution  is  ready 
to  titrate  with  the  previously  prepared  permanganate  solution 
which  is  run  in  drop  by  drop  from  a  burette,  with  constant 
stirring,  until  the  color  (which  disappears  rapidly  at  first,  and 
then  more  slowly)  finally  becomes  permanent,  and  remains  so 
for  one  minute.  The  final  color  should  be  a  light  pink,  and  the 
chemist  should  note  this  color  and  bring  his  subsequent  titra- 
tions  to  the  same  tint.  The  titrations  should  be  performed  in 
a  good  light  and  with  a  white  surface  (piece  of  paper)  under- 
neath the  jar.  Note  carefully  the  quantity  of  permanganate 
solution  used,  and  calculate  its  value  or  standard  as  follows : 
Suppose  0.200  gramme  of  iron  were  taken  and  19.5  cc.  of  the 
permanganate  solution  was  used  :  then 

0.1994  -~  19.5  =  0.010225  -f- . 

Hence  I  cc.  of  permanganate  solution  corresponds  to  .01022 
gramme  of  iron. 

The  results  obtained  on  the  two  samples  of  iron  wire  taken 
should  not  differ  more  than  one  tenth  of  a  cubic  centimetre. 
If  the  difference  is  greater  than  this  more  trials  should  be 
made. 

The  other  method  of  standardizing  the  solution  is  by 
means  of  oxalic  acid.  The  objection  to  this  method  is  the 
uncertainty  of  procuring  a  normal  acid.  When  oxalic  acid  is 
used  the  crystals  should  be  kept  in  a  tight-stoppered  colored- 
glass  bottle,  and  each  bottle  should  be  tested  with  some  per- 
manganate solution,  the  standard  of  which  has  been  previously 
determined,  to  determine  if  it  is  normal.  The  oxalic  method 
has  the  advantage  that  it  is  more  rapid  than  the  iron-wire 
method.  To  standardize  the  solution  by  this  method  weigh 
out  about  250  milligrammes  of  oxalic  acid  on  the  button- 
balance,  the  exact  amount  taken  being  immaterial,  so  that  the 
exact  weight  is  known.  Dissolve  in  water  (about  100  cc.),  and 
add  6  to  8  cc.  of  pure  concentrated  sulphuric  acid.  Heat  to 


I ?2  A    MANUAL    OF  PRACTICAL   ASSAYING. 

about  60°  to  70°  C.,  and  add  permanganate  solution  until  the 
color  is  permanent.  The  color  will  disappear  very  slowly  at 
first,  but  after  a  few  cubic  centimetres  of  the  permanganate 
solution  have  been  added,  it  will  disappear  rapidly.  After  the 
first  faint  permanent  tint  has  formed,  add  one  or  two  drops  of 
permanganate  in  excess  (one  or  two  drops  having  previously 
been  determined  to  be  the  amount  required  to  impart  a  faint 
tint  to  600  cc.  of  distilled  water)  on  account  of  the  greater  bulk 
of  solution  used  when  standardizing  by  iron  wire. 

By  comparing  the  equation  previously  given  with  the  fol- 
lowing equation,  which  represents  the  oxidation  of  oxalic  acid, 

5(H,C,042H30)  +  3H2S04  +  K.Mn.0,  = 

ioCOa  +  2MnSO4  +  K3SO4  +  i8H2O, 

it  will  be  seen  that  the  same  quantity  of  potassium  perman- 
ganate is  required  to  oxidize  one  molecule  of  oxalic  acid  whose 
molecular  weight  is  126,  or  two  atoms  of  iron  (in  the  form  of 
monoxide)  whose  molecular  weight  is  112.  Consequently  we 
have  the  equation  assuming  0.250  gramme  of  oxalic  acid  were 
taken : 

126  :  112  ::  .250  :  .222  -|-. 

V 

In  other  words,  the  250  milligrammes  of  oxalic  acid  taken  rep- 
resented .222+  grammes  of  metallic  iron.  Suppose  that  21.7 
cc.  of  permanganate  solution  were  used,  then  one  cubic  centi- 
metre of  permanganate  solution  would  correspond  to  .01023  -|- 
grammes  of  iron. 

In  practice  the  writer  has  usually  standardized  the  solution 
once  with  iron  wire  and  then  checked  the  result  with  oxalic 
acid,  using  an  acid  which  was  known  to  be  normal. 

Provided  the  proper  precautions  are  observed,  iron  may  be 
determined  in  a  hydrochloric-acid  solution  by  means  of 
standard  potassium-permanganate  solution,  although  most 
authors  claim  that  this  method  is  not  accurate  on  account  of 
the  following  reaction,  which  takes  place  if  the  solution  is  at  all 
warm  : 

KaMnaOe  +  I6HC1  =  2KC1  +  2MnCl,  +  8H2O  +  loCl. 


IRON.  173 

Some  of  the  chlorine  set  free  will  convert  the  ferrous  iron  pres- 
ent into  ferric ;  but  some  will  usually  escape,  and  the  results 
obtained  will  consequently  be  too  high. 

The  writer  has  found  by  experience  that  if  only  a  small 
quantity  of  hydrochloric  acid  is  present  and  the  solution  is  ex- 
tremely dilute  (700  cc.)  and  cold,  and  moreover  contains  a  large 
excess  of  sulphuric  acid  (usually  20  cc.  concentrated  acid),  that 
the  results  obtained  are  as  reliable  as  when  sulphuric  acid  has 
been  used  as  the  solvent.  As  a  further  precaution  some 
chemists  add  a  few  cubic  centimetres  of  a  saturated  solution 
of  manganous  sulphate  before  titration.  The  writer  has 
generally  found  this  latter  precaution  unnecessary,  provided 
the  above  conditions  were  carried  out ;  but  as  the  addition  of 
manganous  sulphate  can  do  no  harm,  it  is  well  to  use  it  when 
the  operator  is  in  doubt  or  when  a  considerable  amount  of 
hydrochloric  acid  has  been  used. 

The  third  method  depends  on  the  fact  that  if  potassium 
bichromate  is  added  to  a  solution  of  a  ferrous  salt  in  the  pres- 
ence of  a  strong  free  acid,  the  ferrous  oxide  is  converted  into 
ferric  oxide,  as  is  shown  by  the  equation 

6FeCla+K2Cr207+i4HCl  =  3Fe3Cl6  +  2KCl  +  Cr3Cl6  +  7H2O, 

which  shows  that  I  or  295.18  parts  of  potassium  bichromate 
will  convert  6  equivalent  or  336  parts  of  iron  to  the  ferric  state 
(295.18  being  the  molecular  weight  of  K2Cr2O7  and  336  being 
6  times  the  atomic  weight  of  Fe).  In  practice  a  half-normal 
solution,  or  a  solution  of  which  one  cubic  centimetre  is  equal 
to  0.005  gramme  of  iron,  is  usually  used.  To  prepare  this 
solution  dissolve  8.785  grammes  of  pure  potassium  bichromate 
in  two  litres  of  water.  The  solution  is  best  standardized  by 
means  of  iron  wire,  dissolving  the  wire  either  in  hydrochloric 
or  sulphuric  acids.  The  solution  is  then  reduced  and  trans- 
ferred to  a  suitable  vessel  for  titration,  some  free  acid  being 
added.  The  bichromate  solution  is  dropped  in  from  a  burette, 
the  liquid  being  constantly  stirred  with  a  glass  rod.  The 
liquid,  which  is  at  first  nearly  colorless,  speedily  acquires  a 


174  A   MANUAL   OF  PRACTICAL   ASSAYING. 

pale-green  tint,  which  changes  gradually  to  a  darker  green. 
A  small  drop  of  the  liquid  is  now  from  time  to  time  taken  out 
by  means  of  the  stirring-rod  and  tested  on  a  porcelain  plate 
with  a  drop  of  potassium  ferricyanide  (free  from  ferrocyanide), 
which  should  not  be  too  strong  or  it  will  give  a  red  precipitate- 
When  the  blue  color  produced  by  the  action  of  a  ferrous  salt 
on  the  ferricyanide  begins  to  lose  the  intensity  which  is 
exhibited  on  the  first  trials  and  becomes  quite  faint,  the 
addition  of  bichromate  solution  is  proceeded  with  more  care- 
fully. When  the  test  no  longer  produces  a  blue  color  the 
oxidation  is  complete.  From  the  remarkable  delicacy  of  the 
reaction  the  exact  point  may  be  easily  hit  to  a  drop.  After  a 
little  practice  a  large  number  of  tests  will  seldom  have  to  be 
made,  as  the  operator  may  determine,  from  the  manner  in 
which  the  green  color  of  the  solution  deepens,  about  how 
much  bichromate  it  will  be  safe  to  add  before  testing.  Many 
authors  (Fresenius,  Cairns,  etc.)  recommend  the  use  of  a 
solution  one  tenth  as  strong  as  the  regular  solution  for  finish- 
ing the  titration.  In  ordinary  practice  this  is  found  to  be 
unnecessary  where  a  solution  as  dilute  as  the  one  recommended 
is  used. 

After  the  titration  is  completed,  take  the  reading  of  the 
burette  and  determine  the  value  of  one  cubic  centimetre  of 
the  solution  in  the  same  way  as  described  for  the  permanganate 
solution.  It  is  best  to  weigh  out  two  portions  of  the  iron  wire 
and  standardize  the  solution  in  duplicate,  as  is  done  in  the  case 
of  the  permanganate  solution. 

For  determining  the  iron  by  this  method  it  may  be  reduced 
to  the  ferrous  state  either  by  means  of  zinc  or  by  means  of  a 
solution  of  stannous  chloride  added  in  slight  excess,  the  excess 
being  taken  up  by  means  of  mercuric  chloride.  This  latter 
method  has  the  advantage  that  the  reduction  may  be  per- 
lormed  in  a  few  moments,  thus  greatly  reducing  the  time 
required  to  make  a  determination.  It  may  also  be  employed 
to  advantage  when  zinc  free  from  iron  and  arsenic  cannot  be 
obtained,  which  may  sometimes  happen.  If  proper  care  is 
used  in  the  reduction  the  result  will  agree  perfectly  with 


IRON.  175 

those  obtained  by  reduction  with  metallic  zinc.  The  only 
point  to  be  observed  is  that  the  solution  of  stannous  and  mer- 
curic chloride  should  not  be  too  strong,  and  only  a  slight  excess 
should  be  used.  The  operator,  after  a  little  practice,  will  have 
no  difficulty  in  observing  these  conditions.  The  best  form, 
and,  on  the  whole,  that  which  gives  the  most  rapid  reduction, 
when  zinc  is  used  to  reduce  the  iron,  is  pure  granulated  zinc. 
The  granulations  should  be  quite  heavy,  otherwise  small  por- 
tions will  become  detached  and  pass  over  with  the  solution  for 
titration  into  the  jar.  The  granulated  zinc  may  be  made  from 
pure  bar  zinc  by  melting  in  a  crucible,  placing  a  few  lumps  of 
charcoal  on  the  surface  of  the  zinc,  and  pouring  into  cold  water 
after  skimming. 

The  solution  may  also  be  reduced  by  boiling  in  a  flask  with 
granulated  zinc  which  has  previously  been  amalgamated  with 
mercury.  In  order  to  amalgamate  the  zinc  place  it  in  sul- 
phuric acid  for  a  few  moments,  remove,  and  wash  with  water; 
then  place  in  a  bottle  containing  clean  mercury  and  sulphuric 
acid,  and  shake.  This  method  of  reduction  has  the  advantage 
that  less  zinc  is  consumed  than  in  the  case  where  raw  zinc  is 
used,  and  also  that  if,  in  transferring  the  solution  from  the  flask, 
some  pieces  of  zinc  pass  over,  they  need  not  be  removed  before 
the  titration  is  proceeded  with,  as  hydrogen  is  not  evolved  from 
the  amalgamated  zinc  in  a  cold  dilute  solution.  It  has  the  dis- 
advantage that  more  time  is  required  to  reduce  the  solution. 
Where  zinc  free  from  impurities  cannot  be  obtained,  the  solu- 
tion may  be  reduced  in  the  following  manner :  Prepare  some 
cubes  of  zinc  about  one-half  inch  square,  and  thoroughly  amal- 
gamate them  with  mercury.  In  each  of  the  flasks  containing 
the  solution  of  iron  to  be  reduced  place  a  strip  of  platinum-foil 
about  three  inches  long  and  three  quarters  of  an  inch  in  width, 
and  on  this  place  a  cube  of  the  amalgamated  zinc.  In  order 
to  have  the  foil  work  well  it  should  be  cleaned  and  its  surface 
roughened.  A  strong  current  of  gas  should  be  induced  by  con- 
tact between  the  zinc  and  platinum.  A  convenient  form  of 
apparatus  for  this  reduction  is  described  in  Vol.  XV,  Trans- 
actions of  the  American  Institute  of  Mining  Engineers.  A 


A    MANUAL    OF  PRACTICAL  ASSAYING. 

good  vessel  to  perform  this  reduction  in  is  the  ordinary  pound 
bottle  that  caustic  potash  and  other  reagents  are  put  up  in  by 
the  manufacturers.  It  has  been  found  by  experiment  that 
-amalgamated  zinc  will  not  give  up  its  iron  until  it  is  nearly 
dissolved.  The  disadvantage  of  this  method  is  the  length  of 
time  it  requires  to  reduce  a  solution — from  6  to  20  hours  gen- 
erally being  necessary.  Several  other  methods  of  reduction 
are  described  by  different  authors,  but  the  above  are  sufficient 
for  every  case  likely  to  occur  in  practice,  and  are  among  the 
best. 

The  exact  method  to  be  pursued  in  making  a  determination 
will  depend  on  the  character  of  the  substance. 

Iron  Ores. —  Most  iron  ores  will  yield  their  iron  by  simple 
boiling  with  acids.  Hydrochloric  acid  is  the  acid  usually  em- 
ployed. Nitric  acid  -is  to  be  avoided,  and  this  is  especially  the 
-case  where  the  iron  is  to  be  determined  volumetrically  by  either 
of  the  above  methods,  for,  if  any  nitric  acid  (which  is  an  oxi- 
dizing agent)  is  present,  reduction  and  subsequent  titration  will 
be  impossible.  If  an  ore  is  not  decomposed  by  simple  boiling 
with  hydrochloric  acid  it  may  be  treated  with  all  three  acids 
in  the  manner  described  for  sulphide  ores. 

Usually  from  0.5  to  i.o  gramme  of  ore  is  dissolved  in  a 
small  casserole  or  beaker,  a  small  vessel  always  being  desirable, 
as  it  avoids  the  use  of  a  large  excess  of  acid ;  and  when  all  the 
iron  is  in  solution,  which  may  be  determined  by  the  appearance 
of  the  insoluble  residue,  the  contents  of  the  vessel  are  washed 
into  a  flask  and  reduced  by  some  one  of  the  methods  described 
.above,  and  the  iron  determined  volumetrically  by  either  of  the 
standard  solutions  in  the  manner  described  above. 

For  the  determination  of  the  iron  the  filtrate  from  the  silica 
•can  be  taken,  always  provided  nitric  acid  has  not  been  used  in 
•dissolving. 

In  some  rare  cases  an  ore  may  be  encountered  which  will  not 
yield  all  of  its  iron  by  treatment  with  acids.  In  such  a  case  a 
very  good  method  of  procedure  is  to  filter  off  and  fuse  the  in- 
soluble residue  with  potassium  bisulphate  (see  Silica,  Chapter 
I),  and  add  the  product  of  the  fusion,  after  solution  in  water, 


IKON.  177 

or  water  together  with  a  few  drops  of  hydrochloric  acid,  to  the 
filtrate  containing  the  greater  portion  of  the  iron. 

In  the  case  of  chromic  and  titaniferous  iron  ores  which  will 
not  readily  dissolve  by  treatment  with  acids,  fuse  the  insoluble 
residue  as  described  in  Chapter  I,  combine  the  filtrate  from  the 
insoluble  residue  and  the  iron,  determine  the  iron  as  above  in 
the  combined  filtrates. 

Manganese  Ores. — Determine  iron  in  the  same  manner  as 
in  iron  ores. 

Limestone,  Clay,  Cement,  etc. — The  iron  is  best  deter- 
mined in  the  filtrate  from  the  silica  (when  the  insoluble  residue 
has  been  fused,  the  filtrate  from  it  should  be  added  to  the  fil- 
trate from  the  fusion)  by  heating  it  and  precipitating  the  iron 
with  ammonia  as  ferric  hydrate.  If  the  iron  alone  is  required 
this  precipitate  should  be  boiled  in  the  beaker  for  a  few  min- 
utes and  then  filtered  and  washed  with  boiling  water.  When 
the  washings  no  longer  show  the  presence  of  chlorides  (this 
can  be  determined  by  obtaining  a  small  portion  of  the  wash- 
ings in  a  test-tube,  acidifying  with  nitric  acid,  and  adding  a 
-drop  of  silver-nitrate  solution,  which  should  not  give  a  white 
precipitate  if  the  chlorides  are  all  removed),  the  precipitate  can 
be  dissolved  with  warm  dilute  sulphuric  acid  directly  into  a 
flask,  the  iron  being  reduced  and  determined  as  before.  Where 
lime,  magnesia,  etc.,  are  not  to  be  determined  in  the  filtrate,  the 
precipitate  need  not  be  washed  to  the  extent  of  removing  the 
last  traces  of  chlorides. 

When  alumina  is  to  be  determined,  proceed  in  the  manner 
described  in  Chapter  XVII,  on  Alumina. 

Sulphide  Ores,  Mattes,  etc. — The  same  method  may  be 
pursued  in  the  case  of  all  sulphide  ores,  no  distinction  being 
made  between  copper  ores,  lead  ores,  iron  ores,  etc.,  except  that, 
when  the  amount  of  iron  present  is  small,  larger  quantities 
should  be  taken.  Dissolve  0.5  gramme  of  ore  in  a  small  casse- 
role with  2  cc.  of  strong  hydrochloric,  5  cc.  strong  nitric,  and 
about  8  cc.  dilute  sulphuric  acids  added  in  the  order  named. 
The  sulphuric  acid  should  be  about  60  per  cent  concentrated 
acid  and  40  per  cent  water.  A  flat-bottomed  flask  can  also  be  used 


A    MANUAL    OF  PRACTICAL   ASSAYING. 

for  the  solution,  the  subsequent  reduction  being  performed  in 
the  same  flask.  Heat  on  a  sand-bath  or  iron  plate  until  dense 
white  fumes  of  SO3  are  evolved.  Continue  to  heat  for  about 
two  or  three  minutes,  in  order  to  be  sure  of  removing  the  last 
traces  of  nitric  acid  ;  remove  from  the  source  of  heat,  cool,  and 
dilute  to  about  30  cc.  If  a  casserole  was  used  for  solution, 
wash  the  contents  into  a  flask,  reduce,  and  determine  volumet- 
rically.  In  the  case  of  lead  ores  the  solution  is  best  reduced 
by  means  of  metallic  zinc,  on  account  of  the  sulphate  of  lead 
which  is  formed.  The  zinc  reduces  this  lead  sulphate  to  me- 
tallic lead,  resulting  in  the  liberation  of  any  small  amount  of 
ferric  sulphate  which  it  might  have  held  mechanically  so  that  it 
would  not  have  been  reduced,  thus  giving  too  low  a  result, 
When  an  ore  contains  arsenic  or  antimony  the  reduced  solution 
cannot  be  safely  titrated  by  means  of  potassium  permanganate. 
In  this  case  it  is  best  to  first  precipitate  the  arsenic  or  antimony^ 
with  sulphuretted  hydrogen,  filter  off  the  precipitated  sul- 
phides, and  determine  the  iron  in  the  filtrate.  In  the  case  of 
copper  ores  containing  large  percentages  of  copper,  it  is  best 
to  first  precipitate  the  iron  with  ammonia  and  determine  as  in 
the  case  of  iron  in  limestones,  as  copper  will  interfere  with  the 
titration  and  give  too  high  results. 

Oxidized  Ores  of  Lead,  Silver,  Copper,  etc. — Treat  in 
the  same  manner  as  an  oxidized  iron  ore. 

Slag. — If  the  sample  has  been  taken  by  suddenly  chilling  it 
(see  Chapter  I,  on  Silica),  it  may  be  treated  as  follows :  Weigh 
out  one  half  gramme  of  finely  pulverized  slag  into  a  casserole 
of  about  100  cc.  capacity,  moisten  with  about  7  cubic  centi- 
metres of  water,  and  stir  with  a  glass  rod.  Then  add  about  $ 
cc.  hydrochloric  acid  and  stir  again  with  a  glass  rod  in  order  to 
break  up  any  clots  which  form  and  stick  to  the  bottom.  Heat 
to  boiling,  and  stir  from  time  to  time,  if  necessary.  When  the 
slag  is  decomposed,  which  may  be  determined  by  moving  the 
glass  rod  around  the  bottom  of  the  casserole  to  see  if  any  gritty 
substance  is  encountered.  If  no  grit  is  encountered  and  the 
insoluble  portion  appears  like  flocculent  silica  when  the  solu- 
tion is  stirred  with  the  rod,  the  slag  is  decomposed.  Usually 


IRON.  179 

there  will  be  some  black  specks  seen  floating  on  the  surface  of 
the  liquid,  but  they  may  be  disregarded,  as  they  consist  princi- 
pally of  lead  sulphide.  The  contents  of  the  casserole  are  now 
diluted  with  water  and  a  few  cubic  centimetres  of  dilute  sul 
phuric  acid  added,  and  then  some  pure  zinc  to  reduce  the  iron, 
the  casserole  being  covered  with  a  convex  watch-glass.  After 
the  iron  is  reduced,  which  will  only  require  a  few  minutes,  as 
tmost  of  the  iron  was  originally  present  as  ferrous  iron,  and  if 
the  solution  is  performed  rapidly,  but  a  small  portion  of  it  will 
have  become  oxidized  ;  it  can  be  determined  by  either  of  the 
methods  of  titration  given, — standard  bichromate  or  perman- 
ganate of  potassium  solution.  Or  the  iron  may  be  reduced  by 
means  of  stannous  chloride  as  before  described,  and  determined 
with  standard  bichromate  solution.  A  determination  may  be 
made  in  from  ten  to  fifteen  minutes,  according  to  the  method 
employed.  When  the  sample  was  not  so  taken  that  the  slag 
will  decompose  in  hydrochloric  acid  a  cintering  fusion  may  be 
made  on  0.5  gramme  (see  Chapter  I),  the  fusion  being 
dissolved  in  water  and  hydrochloric  acid,  and  the  iron  deter- 
mined as  above,  or  the  iron  may  be  determined  in  the  filtrate 
from  the  silica.  If  the  iron  is  determined  in  the  filtrate  from 
the  silica,  care  should  be  taken  not  to  heat  the  mass,  after 
evaporation  to  dryness,  much  above  110°  C.,  otherwise  chloride 
of  iron  will  be  volatilized.  Objection  may  be  taken  to  the 
above  rapid  method  on  the  ground  that  it  is  not  absolutely 
accurate.  However,  with  ordinary  care  in  manipulation  dupli- 
cates will  agree  within  two  tenths  of  a  per  cent,  and  the 
method  certainly  gives  results  sufficiently  accurate  for  the  con- 
trol of  the  workings  of  the  furnace  in  a  metallurgical  works. 
The  writer  has  frequently  examined  the  insoluble  residue  from 
the  silica  determination  for  iron  by  fusing,  without  finding 
more  than  a  trace,  and  generally  without  being  able  to  detect 
any  ferrous  oxide.  On  account  of  the  rapidity  of  this  method 
it  is  invaluable  to  the  lead  or  copper  metallurgist  for  the  con- 
trol of  the  workings  of  the  furnace. 

Fused   Ores,   Fused   Flue-dust,   etc. —  These  will    fre- 
quently decompose  as  perfectly  as  a  slag  if  sampled  by  the 


I  SO  A    MANUAL    OF  PRACTICAL   ASSAYING. 

rod  (see  Part  II,  Chapter  I).  In  such  a  case  the  iron  may  be 
determined  as  above.  When  the  insoluble  residue  is  gritty 
and  contains  iron  it  should  be  fused  either  with  acid  sulphate 
of  potassium  or  carbonate  of  soda,  the  determination  then 
being  proceeded  with  as  described  under  the  head  of  Iron  Ores, 
the  filtrate  from  the  insoluble  residue  and  the  silica  being  com- 
bined. 

Pig-iron,  etc. — Most  pig-irons,  steels,  etc.,  will  give  up 
their  iron  by  simple  heating  with  dilute  sulphuric  acid.  The 
iron  may  then  be  determined  as  easily  as  in  the  case  of  piano- 
forte wire,  it  however  being  a  good  plan  where  0.5  gramme 
is  taken  to  dilute  the  solution  up  to  500  cc.  with  distilled 
water,  draw  off  two  or  three  portions  of  100  cc.  each  with  a 
pipette,  reduce  each  portion,  and  determine.  A  very  good  plan 
is  to  titrate  one  portion,  then  add  the  next  portion  to  the 
same  solution  and  titrate,  then  add  the  third  portion,  and  take 
the  total  reading  of  the  burette,  making  the  calculation  of  the 
percentage  on  the  basis  of  three  fifths  of  a  gramme  of  sub- 
stance taken. 

In  the  case  of  ores,  etc.,  containing  arsenic  and  antimony 
the  following  rapid  method  will  serve  for  all  technical  deter- 
minations: Decompose  as  described  above,  and  reduce  the 
iron  with  granulated  zinc.  When  the  iron  is  all  reduced  filter 
rapidly,  and  wash  thoroughly  with  water.  The  arsenic  and 
antimony  will  be  precipitated  by  the  zinc  and  remain  on  the 
filter.  The  filtrate  containing  the  iron  can  now  be  safely 
titrated  as  above. 

Zimmermann-Reinhardt  Method. — The  following  modi- 
fication of  this  method*  is  extensively  used  in  the  Lake 
Superior  iron  region  for  the  estimation  of  the  iron  in  ores.  As 
the  method  is  extremely  rapid  (a  determination  can  be  made 
in  10  minutes)  and  sufficiently  accurate  for  all  commercial  pur- 
poses, it  is  highly  recommended. 

The  following  solutions  are  necessary  : 

Stannous  Chloride. — One  pound  of  stannous  chloride  is 

*  Journal  of  the  Am.  Chem.  Society,  Vol.  XVII,  No.  5,  May,  1895. 


IRON. 

dissolved  in  one  pound  of  hydrochloric  acid  (sp.  gr.  1.2),  slightly 
diluted  with  water,  and  when  solution  is  effected,  is  diluted  to 
two  liters. 

Hydrochloric  Acid. — Made  by  mixing  equal  volumes  of 
strong  acid  and  water  (sp.  gr.  i.i). 

Mercuric  Chloride.— A  saturated  solution  is  prepared  by 
dissolving  the  salt  in  hot  water,  and,  after  allowing  to  cool  and 
crystallize,  filtering. 

Manganous  Sulphate. — One  hundred  and  sixty  grammes 
of  manganous  sulphate  are  dissolved  in  water  and  diluted  to 
1750  cc.  To  this  are  added  330  cc.  of  phosphoric  acid  (syrup 
1.7  sp.  gr.)  and  320  cc.  of  sulphuric  acid  (sp.  gr.  1.84). 

One-half  gramme  of  ore  is  treated  in  a  beaker  with  two 
and  a  half  cc.  of  stannous-chloride  and  ten  cc.  of  the  hydro- 
chloric-acid solutions.  The  beaker  is  covered  with  a  watch- 
glass  and  its  contents  allowed  to  boil  gently  on  an  iron  plate 
until  the  ore  is  completely  dissolved.  As  soon  as  solution  is 
effected  stannous  chloride  is  run  in  from  a  burette,  drop  by 
drop,  until  the  iron  is  completely  reduced,  the  reduction  being 
indicated  by  the  disappearance  of  the  greenish-yellow  color. 
The  solution  is  now  slightly  oxidized  with  a  few  drops  of  the 
potassium-permanganate  solution  and  "kept  warm.  Just  before 
titration  the  final  reduction  is  effected  by  the  addition  of  a 
drop  or  two  of  the  stannous-chloride  solution,  avoiding  any 
considerable  excess.  The  sides  of  the  beaker  are  washed  down 
and  five  cc.  of  the  mercuric-chloride  solution  are  added  to  take 
up  the  excess  of  stannous-chloride.  The  contents  of  the  beaker 
are  now  washed  into  a  500  cc.  beaker,  in  which  has  been  placed 
six  to  eight  cc.  of  the  manganous-sulphate  solution  and  about 
400  cc.  of  water. 

The  titration  is  now  proceeded  with,  using  a  standard  solu- 
tion of  potassium  permanganate  (see  page  169). 

Ores  Containing  Organic  Matter. — If  the  amount  of 
organic  matter  is  small  it  may  be  oxidized,  during  solution,  by 
the  addition  of  potassium  chlorate.  If  the  amount  is  large  it 
is  best  to  burn  off  and  follow  with  the  regular  method. 


A    MANUAL    OF  PRACTICAL   ASSAYING. 

Pyritous  Ores. — These  may  be  treated  as  in  the  case  of 
ores  containing  organic  matter. 

Magnetites. — As  magnetites  are  frequently  difficult  to 
decompose,  it  is  best  to  make  a  fusion  with  mixed  carbonates, 
and,  after  dissolving  from  the  crucible  with  a  little  water, 
proceed  as  above. 

Jones  Method. — This  method  is  due  to  Prof.  L.  J.  W. 
Jones,,*  and  will  be  found  extremely  useful,  especially  where 
zinc  for  reduction  which  is  free  from  arsenic  and  iron  cannot 
be  obtained. 

A  hydrochloric  acid  solution  of  the  ore  is  prepared  in  the 
usual  manner.  To  this  solution  add  about  20  grammes  of 
test  lead,  and  boil  for  from  5  to  8  minutes,  according  to  the 
amount  of  iron  present.  The  iron  is  reduced  according  to  the 
equation 

FeaCl6+  Pb  =  2  Fed,  +  PbCl2 , 

and  may  be  determined  by  titration  with  standard  potassium 
dichromate  solution  in  the  usual  manner.  The  results  are 
excellent.  There  are  no  interferences.  Arsenic,  antimony 
and  copper  which  interfere  with  other  methods  are  harmless. 

Proceedings  Colo.  Scientific  Society,  1896'. 


CHAPTER  XVII. 
ALUMINIUM  (Al). 

ONLY  two  methods  are  in  general  use  for  the  determination 
of  aluminium  (Al)  or  alumina  (AlaO3) :  1st.  Precipitation  of 
the  alumina  as  hydroxide  with  ammonia,  filtration  of  the  pre- 
cipitate, ignition  to  Al2O3,and  weighing  as  such;  2d.  Direct 
determination  as  aluminium  phosphate  (A12P2O/). 

First  Method. — This  method  presents  the  disadvantages 
common  to  all  indirect  methods,  and  is  quite  tedious,  espe- 
cially in  the  case  of  a  substance  containing  iron,  phosphorus, 
chromium,  titanium,  etc. 

The  method  of  procedure  is  as  follows:  The  silica,  and  all 
metals  of  the  sulphuretted-hydrogen  group  (As,  Sb,  Sn,  Pb,  Hg, 
Cu,  Bi,  and  Cd),  if  present,  must  be  removed  from  the  solution,. 
The  silica  is  removed  by  any  of  the  methods  described  in  Part 
II,  Chapter  I.  The  metals  of  the  sulphuretted-hydrogen  group 
can  be  removed  by  passing  a  rapid  current  of  sulphuretted- 
hydrogen  gas  through  the  filtrate  from  the  silica,  the  precau- 
tion being  observed  that  nitric  acid  is  not  present.  After  the 
sulphides  are  all  precipitated,  the  solution  should  be  rapidly 
filtered,  and  the  beaker  and  precipitate  on  the  filter  should 
be  thoroughly  washed  with  distilled  water,  to  which  has  been 
added  some  sulphuretted-hydrogen  water.  Should  a  precipi- 
tate of  sulphides  form  in  the  filtrate,  the  solution  should  be 
again  treated  with  sulphuretted-hydrogen  gas  until  a  precipitate 
no  longer  forms.  The  filtrate  from  the  precipitated  sulphides  is 
heated  to  boiling,  and  the  sulphur  is  oxidized  by  the  addition 
of  potassium  chlorate  or  bromine-water,  which  should  be  added 
from  time  to  time  until  the  solution  is  perfectly  clear.  Should 

181 


1 82  A    MANUAL    OF  PRACTICAL   ASSAYING. 

a  precipitate  form  upon  boiling  (if  much  sulphuretted  hydrogen 
was  used  yellow  sulphur  will  separate),  it  should  be  filtered  off. 

The  solution  is  now  ready  for  the  precipitation  of  the 
aluminium  as  hydroxide  with  ammonia,  which  is  effected  as 
follows :  Ammonia  in  slight  excess  is  added  to  the  solution, 
and  the  contents  of  the  beaker  are  boiled  until  the  free  ammo, 
nia  is  driven  off.  This  can  be  determined  by  holding  a  piece 
of  glass,  previously  moistened  with  dilute  hydrochloric  acid, 
over  the  beaker;  should  no  white  fumes  form  the  free  ammonia 
has  been  expelled.  It  is  essential  that  the  free  ammonia  should 
be  expelled,  as  aluminium  hydroxide  is  slightly  soluble  in  an 
excess  of  ammonia.  It  is  also  essential  that  ammonium  chlo- 
ride be  present ;  sufficient  will  be  formed  when  the  ammonia  is 
added  if  the  solution  contains  much  hydrochloric  acid.  The 
contents  of  the  beaker  are  now  ready  for  filtration,  which  is 
performed  as  usual,  washing  the  precipitate  thoroughly  with 
hot  water.  Add  a  little  ammonia  to  the  filtrate,  and  boil. 
Should  a  precipitate,  form,  filter  it  off,  and  add  it  to  the  first 
precipitate.  This  is  essential,  as  when  the  amount  of  alumina 
present  is  large  it  may  not'  all  be  precipitated  the  first  time. 

The  precipitate  will  consist  of  aluminium  hydroxide,  ferric 
hydroxide,  if  any  iron  was  present  in  the  solution  (iron  is  gener- 
ally present) ;  chromium  hydroxide,  provided  chromium  was 
present  in  the  solution  (except  in  the  case  of  chromic  iron  ores 
and  chrome  iron  and  steel,  chromium  will  rarely  be  encoun- 
tered) ;  and  also  of  phosphoric  acid,  which  is  present  in  all  iron 
ores.  The  precipitate  is  now  dried  in  an  air-bath  or  by  placing 
the  funnel  with  the  filter  in  a  ring-stand  over  a  sand-bath  or 
hot  plate.  When  dry  the  precipitate  is  transferred  to  a  weighed 
platinum  crucible  by  removing  the  filter  from  the  funnel, 
inverting  it  over  the  crucible,  and  rolling  it  between  the  fingers. 
The  filter  is  rolled  into  a  ball,  and  placed  upon  the  lid  of  the 
crucible,  where  it  is  burned  and  ignited  over  the  flame  of  a 
burner.  The  contents  of  the  lid  are  now  added  to  the  contents 
of  the  crucible,  and  the  whole  moistened  with  a  few  drops  of 
nitric  acid,  the  addition  of  nitric  acid  being  necessary  in  order 
to  oxidize  any  iron  to  the  ferric  form  which  might  have  been 


ALUMINIUM.  183 

reduced  by  the  carbon  of  the  filter-paper.  A  second  addition 
of  nitric  acid,  and  a  second  ignition,  is  necessary  where  much 
iron  is  present  and  a  large  filter-paper  has  been  used.  The 
crucible  and  its  contents  are  now  ignited  over  the  blast-lamp 
or  in  the  muffle-furnace  at  a  bright-red  heat,  cooled,  and 
weighed.  The  increase  in  weight  of  the  crucible  represents 
the  weight  of  the  combined  alumina  (A12O3),  ferric  oxide 
(Fe2O3),  phosphoric  acid  (PaO6),  and  chromic  acid  (CraO3). 

From  the  weight  of  the  combined  oxides  calculate  the 
percentage.  From  this  percentage  deduct  the  percentages  of 
the  different  oxides,  as  determined,  in  separate  portions.  Ex- 
cept in  the  case  of  chromic  titaniferousand  phosphoric  iron  ores, 
the  difference  between  the  percentage  of  the  combined  oxides 
and  the  percentage  of  ferric  oxide  will  be  the  percentage  of 
alumina  present.  The  percentage  of  ferric  oxide  present  in  the 
combined  oxides  may  be  determined  as  follows :  Transfer  the 
combined  oxides,  after  weighing,  to  an  agate  mortar,  and  grind 
to  an  impalpable  powder.  Weigh  out  a  portion  of  the  powder, 
and  fuse  it  with  acid  potassium  sulphate  in  the  manner  de- 
scribed in  Chapter  I.  Dissolve  the  fused  mass  in  hot  water, 
add  an  excess  of  sulphuric  acid,  reduce,  and  determine  the 
iron  as  described  in  Chapter  XVI.  From  the  weight  of  the 
ferric  oxide,  as  thus  determined,  calculate  the  total  weight  of 
the  ferric  oxide  present  in  the  combined  oxides,  and  deduct 
it  from  the  weight  of  the  combined  oxides,  the  difference 
being  the  weight  of  alumina  in  the  amount  of  substance  taken 
for  analysis.  When  extreme  accuracy  is  required  the  author 
prefers  this  method  to  the  determination  of  the  iron  in  a  sepa- 
rate portion,  and  deducting  that  result  from  the  weight  of 
the  combined  oxides. 

Iron  Ores. — Dissolve  as  in  Chapter  XVI.  The  treatment 
with  sulphuretted  hydrogen  can  usually  be  omitted,  as  metals 
of  the  sulphuretted-hydrogen  group  are  seldom  present.  To 
the  filtrate  from  the  silica  add  ammonia  and  proceed  as  above. 
When  titanium  and  chromium  are.  present  they  will  be  precipi- 
tated with  the  alumina.  In  this  case  proceed  as  described  in 
Chapters  XVIII  and  XIX,  or  by  the  second  method. 


184  A   MANUAL   OF  PRACTICAL  ASSAYING. 

Manganese  Ores. — Same  treatment  as  with  iron  ores,  ex~ 
cept  that  it  is  necessary  to  dissolve  the  first  precipitate  of 
hydroxides  with  a  little  hydrochloric  acid  and  reprecipitate 
-with  ammonia,  in  order  to  insure  the  separation  of  the  man- 
ganese. 

Limestones,  Clays,  Cements,  etc. — Same  treatment  as  in  the 
case  of  iron  ores,  taking  the  filtrate  from  the  silica  obtained 
as  described  in  Chapter  I.  When  a  fusion  of  the  insoluble 
residue  has  been  necessary,  combine  the  filtrates  from  the  in- 
soluble and  the  silica.  As  the  alumina  is  generally  present  as 
a  silicate,  it  can  be  determined  in  these  substances,  with  a 
sufficient  degree  of  accuracy  for  technical  purposes,  as  fol- 
lows :  Determine  the  insoluble  residue  (see  Chapter  I),  and 
-after  weighing  it  fuse  and  determine  the  silica.  The  differ- 
ence between  the  weights  of  the  insoluble  residue  and  silica 
obtained  will  be  the  weight  of  alumina  present.  When  barium 
is. present  the  weight  of  the  barium  sulphate  should  also  be 
determined  and  deducted  from  the  weight  of  the  insoluble 
residue. 

Silver  and  Lead  Ores. — It  will  generally  be  sufficient  to 
•determine  the  insoluble  residue  (Chapter  I)  and  the  alumina 
by  difference  as  in  the  case  of  clays.  When  the  ore  contains 
compounds  of  alumina  which  are  soluble  in  acids,  the  filtrate 
from  the  silica,  obtained  by  fusion,  should  be  added  to  the 
filtrate  from  the  insoluble  residue,  and  the  alumina  determined 
in  the  combined  solutions  as  above.  In  the  case  of  lead  ores 
which  do  not  contain  any  members  of  the  sulphuretted-hydro- 
gen group,  except  lead,  the  following  method  may  be  adopted: 
Determine  the  insoluble  residue  by  treating  with  hydrochloric, 
nitric,  and  sulphuric  acids  and  evaporation  to  fumes  of  sulphuric 
anhydride.  The  lead  will  all  be  converted  into  sulphate,  and 
can  be  removed  from  the  insoluble  residue  with  ammonium 
acetate.  The  filtrate  from  the  insoluble  residue  and  lead  sul- 
phate will  now  be  free  from  lead,  and  the  treatment  with  sul- 
phuretted hydrogen  can  be  omitted. 

Slags,  Mattes,  etc. — Determine  the  alumina  in  the  filtrate 
from  the  silica  as  above.  In  the  case  of  lead  and  copper  slags 


ALUMINIUM.  185 

and  mattes  these  metals  will  have  to  be  removed  by  treatment 
with  sulphuretted  hydrogen.  When  much  manganese  or  zinc 
is  present,  it  will  be  necessary  to  redissolve  the  first  precipitate 
of  hydroxides  in  a  little  hydrochloric  acid  and  reprecipitate 
with  ammonia.  If  this  precaution  is  omitted  the  results  will 
be  high,  on  adcount  of  the  manganese  and  zinc  carried  down 
with  the  iron  and  alumina.  A  better  method  is  to  make  a 
basic-acetate  precipitation,  dissolve  the  filtered  and  washed 
precipitate  with  a  little  hydrochloric  acid,  arid  reprecipitate 
with  ammonia  as  above. 

Second  Method. — This  method,  which  was  proposed  by 
Dr.  Drown,*  depends  upon  the  principle  that  if  a  slightly  acid 
solution  of  aluminium  and  iron  is  electrolyzed  with  an  anode 
of  platinum  and  a  mercury  cathode,  the  iron  will  be  precipi- 
tated on  the  mercury,  and  the  solution,  after  precipitation  of 
the  iron,  will  contain  all  the  aluminium,  from  which  it  (the  Al) 
may  be  readily  precipitated  as  a  phosphate.  This  method  is 
particularly  adapted  to  the  analysis  of  alloys  containing  com- 
paratively small  quantities  of  aluminium  and  considerable  iron. 
The  method  of  procedure  in  the  case  of  an  iron  or  steel  is  as 
follows :  Dissolve  from  5  to  10  grammes  of  the  substance  in 
sulphuric  acid,  evaporate  until  white  fumes  of  sulphuric 
anhydride  appear,  add  water,  heat  to  bring  the  iron  into  solu- 
tion, filter  off  the  silica  and  carbon,  and  wash  with  water  acid- 
ulated with  sulphuric  acid.  Render  the  filtrate  nearly  neutral 
with  ammonia,  and  add  to  the  beaker,  in  which  the  electrolysis 
is  to  be  made,  about  one  hundred  times  as  much  mercury  as 
the  weight  of  iron  or  steel  taken.  The  bulk  of  the  solution 
should  be  from  300  to  500  cc.  Connect  with  the  battery  or 
dynamo  current  so  that  about  two  amperes  will  pass  through 
the  solution  over  night.  The  connection  with  the  mercury  is 
best  made  by  means  of  a  platinum  wire  fused  into  a  piece  of 
glass  tubing  which  passes  through  the  solution.  The  glass  tube 
should  be  filled  for  about  one  inch  with  mercury  in  order  to 

*  Transactions  of  The  American   Institute  of  Mining  Engineers  Vol.  XX, 
page  242. 


1 86  A    MANUAL    OF  PRACTICAL   ASSAYING. 

weight  it  and  make  a  perfect  connection  with  the  mercury  irj> 
the  beaker.  In  the  morning  the  solution  is  tested  for  iron,  and 
if  necessary  the  electrolysis  is  continued  after  adding  sufficient 
ammonia  to  neutralize  the  acid  set  free  by  the  deposition  of 
the  iron.  The  progress  of  the  operation  may  be  observed  by 
the  change  in  color  of  the  solution.  At  first  it  becomes  darker 
in  color  near  the  anode ;  after  five  or  six  hours  it  is  nearly 
colorless,  and  finally  becomes  pink,  from  the  formation  of  per- 
manganate. 

When  the  solution  gives  no  reaction  for  iron,  upon  testing, 
it  is  removed  from  the  beaker  by  means  of  a  pipette  while  the 
current  is  still  passing.  When  as  much  as  possible  has  been 
removed  without  breaking  the  .current,  water  is  added  and 
drawn  off  by  the  pipette  as  before.  When  the  solution  has 
been  treated  in  this  manner  until  there  is  no  longer  danger  of 
resolution  of  the  precipitated  iron,  the  current  is  broken  and 
the  mercury  is  thoroughly  washed  with  water  until  the  last 
traces  of  the  solution  have  been  removed.  Should  the  solution 
not  be  perfectly  clear,  sometimes  there  will  be  a  separation  of 
oxide  of  manganese;  it  should  be  filtered.  The  solution  is  now 
made  nearly  neutral  with  ammonia,  sodium  phosphate  in  excess, 
and  about  10  grammes  of  sodium  acetate  are  added,  and  the 
solution  is  boiled  for  at  least  forty  minutes.  The  aluminium 
will  be  precipitated  as  a  phosphate,  which  precipitate  is  filtered, 
washed,  dried,  ignited,  and  weighed.  The  ignited  aluminium 
phosphate  should  be  white.  If  it  has  more  than  the  faintest 
shade  of  color  (due  to  iron),  it  should  be  fused  with  acid  potas- 
sium sulphate,  the  fused  mass  being  brought  into  solution  with 
water  and  a  little  sulphuric  acid,  the  solution  finally  being 
electrolyzed  for  2  or  3  hours.  The  solution  now  free  from  iron 
is  drawn  off  and  the  aluminium  is  precipitated  as  a  phosphate 
as  before.  This  second  precipitate  will  be  pure.  Drown  states 
that  he  has  generally  found  the  first  precipitate  of  such  purity 
that  this  treatment  and  second  precipitation  are  unnecessary. 
Drown  states  the  ignited  precipitate  to  have  the  composition 
7AlaO3,  6P2O6,  in  place  of  A1PO4,  and  consequently  gives  24.14 
as  the  percentage  of  aluminium. 


ALUMINIUM.  187 

This  method  also  answers  for  the  determination  of  iron. 
If  the  iron  is  to  be  determined  the  mercury  is  weighed  before 
proceeding  with  the  electrolysis,  and  after  electrolyzing  wash- 
ing and  decanting,  it  is  dried  for  a  few  minutes  at  a  tempera- 
ture of  IOO°  to  110°  C.  and  weighed  again.  The  increase  in 
weight  of  the  mercury  represents  the  weight  of  iron  in  the 
amount  of  substance  taken.  As  mercury  loses  weight  upon 
drying,  even  at  such  a  low  temperature  as  100°  C,  and  there 
is  generally  a  loss  in  weight  owing  to  the  impurities  in  the 
mercury  which  pass  into  solution,  it  is  best  to  run  a  blank 
beaker,  containing  about  the  same  weight  of  mercury  as  is 
used  in  the  analysis,  and  water  slightly  acidulated  with  sul- 
phuric acid,  in  the  circuit  with  the  analyses.  The  loss  in 
weight  of  the  mercury  used  in  the  blank  should  be  added  to 
the  results  in  the  case  of  each  iron  determination. 

This  method  may  also  be  used  for  the  determination  ot 
iron  and  aluminium  in  ores,  etc. 


CHAPTER  XVIII. 
CHROMIUM   (Cr). 

CHROMIUM  is  always  determined  as  chromic  oxide  (CruO3), 
dark  green  in  color. 

The  only  determinations  of  chromium  which  the  metallur- 
gical chemist  will  be  called  upon  to  make  are  in  iron  ores 
(especially  chromic  iron  ore,  known  as  chromite,  or  mag- 
netite, which  sometimes  contain  chromium),  pig-iron,  and  steel. 

Ores. — Fuse  from  i.o  to  2.0  grammes  of  ore  with  5  to  10 
grammes  of  mixed  carbonates  of  sodium  and  potassium  and 
I  gramme  of  sodium  nitrate  (see  Part  II,  Chapter  I).  Dissolve 
the  fused  mass  in  water  and  hydrochloric  acid  in  slight  excess, 
evaporate  to  dryness,  and  determine  the  silica  in  the  usual  way. 
To  the  filtrate  from  the  silica  add  sodium  carbonate  until  it 
is  strongly  alkaline,  and  then,  without  filtering  out  the  precipi- 
tate, bromine  water  until  the  solution  is  deeply  colored,  stirring 
continually.  Now  add  3  cc.  of  pure  bromine  and  heat  for  one 
hour,  with  frequent  stirring,  keeping  the  solution  alkaline  and 
gradually  increasing  the  heat  until  it  boils.  Allow  to  boil  for  an 
hour,  when  the  chromic  oxide  should  all  be  oxidized  to  chromic 
acid.  Now  filter  (precipitate  A)  and  wash  thoroughly  with  hot 
water,  washing  first  by  decantation  and  then  on  the  filter  until 
f  the  filtrate  runs  through  colorless.  Should  the  ore  contain  a 
large  amount  of  chromium,  in  order  to  insure  its  complete  sepa- 
ration, wash  the  precipitate  on  the  filter  back  into  the  beaker 
with  the  wash-bottle,  bring  the  bulk  of  the  solution  up  to  about 
100  cc.  with  water,  add  2  cc.  of  bromine,  and  proceed  as  before, 
filtering  through  the  same  filter.  The  filtrate  will  now  contain 
all  of  the  chromium  as  alkaline  chromate,  and  probably  some 

1 88 


CHROMIUM.  189* 

of  the  manganese.  The  precipitate  will  contain  all  of  the 
other  constituents  of  the  ore.  Partially  neutralize  the  filtrate 
with  nitric  acid,  add  from  I  to  3  grammes  of  ammonium 
nitrate,  and  evaporate  until  no  odor  of  ammonia  is  perceptible. 
Dilute  with  water,  and  should  a  precipitate  form  (precipitate  B,. 
probably  MnOa,  SiO2,  A12OS,  and  TiO2),  filter,  and  wash  with 
warm  water.  Acidify  the  filtrate  with  hydrochloric  acid,  and 
saturate  it  with  sulphuretted  hydrogen  to  reduce  the  chromic 
acid  to  sesquioxide.  Filter  out  the  precipitated  sulphur  and 
wash.  In  the  filtrate  precipitate  the  chromic  hydroxide  with 
ammonia,  filter,  wash,  dry,  ignite,  and  weigh  the  chromic 
oxide  (Cr2O3).  To  obtain  the  weight  of  the  chromium  multiply 
the  weight  of  the  precipitate  by  0.68586. 

Pig-iron,  Steel,  etc. — Dissolve  the  alloy  in  nitric  and 
hydrochloric  acids,  evaporate  to  dryness,  dry,  and  ignite  the 
insoluble  residue.  Fuse  the  insoluble  residue  with  mixed  car- 
bonates and  proceed  as,  above. 

Titaniferous  Ores  containing  Chromium. — Proceed  as 
described  in  Part  II,  Chapter  XIX  (Titanium),  for  the  deter- 
mination of  the  silica.  Treat  the  filtrate  from  the  silica  as 
described  above  for  the  determination  of  the  chromium.  For 
the  determination  of  the  iron  and  titanium  combine  precipitate 
B  (should  one  form)  with  the  sodium-carbonate  precipitate  A. 
Dissolve  the  combined  precipitates  in  hydrochloric  acid,  and 
proceed  to  determine  the  titanium  as  described  in  Chapter 
XIX  (Ti). 

Determine  the  iron  in  the  filtrate  as  described  in  Chapter 
XIX  (Ti)  and  Chapter  XVI  (Fe). 


CHAPTER   XIX. 
TITANIUM  (Ti). 

TITANIUM  is  generally  determined  by  the  gravimetric 
method  as  titanic  oxide,  but  may  also  be  determined  by  the 
colorimetric  method. 

About  the  only  determinations  of  titanium  which  the  metal- 
lurgical chemist  will  be  called  upon  to  make  are  the  determina- 
tions in  iron  ores  (especially  some  magnetites),  in  pig-iron,  and 
occasionally  steel. 

When  titanium  is  present  the  method  of  determining  the 
iron  and  silica  in  iron  ores,  pig-iron,  etc.,  will  have  to  be  modi- 
fied, and  the  titanium  first  separated  according  to  the  gravi- 
metric method  described  below. 

Colorimetric  Method. — This  method  is  due  to  Weller,* 
and  the  improvements  to  H.  L.  Wells  f  and  W.  A.  Noyes.J 

Mix  o.i  gramme  of  ore  with  0.2  gramme  of  sodium  fluoride, 
both  finely  powdered,  in  a  platinum  crucible.  Add  3  grammes 
of  sodium  pyrosulphate  without  mixing.  Fuse  carefully  and 
heat  gently  until  the  effervescence  ceases  and  copious  fumes 
of  sulphuric  acid  are  evolved.  This  should  take  two  to 
three  minutes.  When  cold  the  mass  in  the  crucible  is  dissolved 
;in  from  15  to  20  cc.  of  cold  water,  and  the  solution  filtered  and 
washed  slightly.  If  a  residue  remains  it  can  be  treated  again 
by  the  same  method  after  burning  it  on  the  filter,  but  the 
amount  of  titanium  usually  found  by  a  second  fusion  is  small. 

To  the  solution,  as  obtained  above,  I  cc.  of  hydrogen  per- 

*  Berichte  d.  Chem.  Ges.,  1882,  p.  2592. 

f  Trans.  Am.  Inst.  of  Mining  Engineers,  Vol.  XIV,  p.  763. 

J  Journal  of  Analytical  and  Applied  Chemistry,  Jan.  1891. 

190 


TITANIUM.  IQI 

oxide  and  a  few  cc.  of  dilute  sulphuric  acid  are  added,  when 
the  solution  is  ready  for  comparison  with  a  solution  containing 
a  known  amount  of  titanium.  For  a  standard  solution  titanic 
oxide  is  dissolved  in  hot  concentrated  sulphuric  acid,  and  the 
solution  diluted  with  dilute  sulphuric  acid  at  first  (to  prevent 
the  precipitation  of  titanic  oxide),  and  then  with  water  until 
I  cubic  centimetre  contains  I  milligramme  of  TiO2. 

As  iron  affects  the  color  of  the  solution,  ferric  sulphate, 
approximately  in  the  same  proportion  as  iron  is  present  in  the 
ore,  should  be  added  to  the  standard  solution.  A  solution  of 
iron-ammonium  alum  answers  well  for  this  purpose,  and,  if  the 
amount  of  iron  in  the  ore  is  not  known,  all  that  is  necessary  is 
to  match  the  color  of  the  solution  of  the  mineral  before  adding 
the  hydrogen  peroxide  to  it.  Small  quantities  of  titanium  in 
the  presence  of  large  quantities  of  iron  can  be  readily  deter- 
mined by  this  method,  which  is  especially  adapted  for  technical 
determinations. 

Gravimetric  Method. — For  the  technical  estimation  of 
titanium  in  iron  ores,  pig-iron,  etc.,  the  following  method  is  as 
rapid  and  accurate  as  any :  * 

Iron  Ores. — Fuse  i.o  gramme  of  finely  pulverized  ore  with 
10  grammes  of  pure  potassium  bisulphate  in  a  large  platinum 
crucible,  heating  the  covered  crucible  over  a  very  low  flame 
until  the  bisulphate  is  melted.  This  operation  must  be  care- 
fully conducted,  as  there  is  danger  of  the  bisulphate  boiling 
over,  and  also  loss  from  spirting.  Raise  the  heat  very  gradu- 
ally, keeping  the  mass  just  liquid  and  the  temperature  at  the 
point  at  which  slight  fumes  of  sulphuric  anhydride  are  given 
off  when  the  lid  is  slightly  raised,  until  the  bottom  of  the  cru- 
cible is  dull  red.  When  the  ore  is  completely  decomposed, 
remove  the  heat,  take  off  the  crucible  lid,  and  incline  the 
crucible  at  such  an  angle  that  the  fused  mass  will  run  together 
on  one  side  of  the  crucible  and  as  near  the  top  as  possible. 
Allow  it  to  cool  in  this  position  ;  when  cold  it  is  easily  de- 
tached from  the  crucible.  Place  the  crucible  and  lid  in  a 
beaker  (No.  4)  half  full  of  cold  water,  and  the  fused  mass  in  a 

*  Blair's  "Chemical  Analysis  of  Iron."     Tenth  Census  U.  S.,  Vol.  XV,  p.  512. 


I92  A   MANUAL    OF  PRACTICAL  ASSAYING. 

small  platinum  tray  or  basket  suspended  in  the  beaker.  Pour 
into  the  beaker  sufficient  strong  aqueous  solution  of  sulphur- 
ous acid  to  raise  the  liquid  to  the  top  of  the  basket,  and  allow 
the  fusion  to  dissolve,  which  may  require  twelve  hours.  Re- 
move the  crucible,  lid,  and  basket,  washing  off  with  a  jet  of 
cold  water.  Stir  the  solution,  which  should  smell  strongly  of 
sulphurous  acid,  and  allow  the  insoluble  matter  to  settle.  Filter, 
wash,  dry,  ignite,  and  weigh  the  insoluble  residue.  Treat  with 
hydrofluoric  acid  and  a  few  drops  of  sulphuric  acid,  evaporate 
to  dryness,  ignite,  and  weigh,  the  loss  being  silica.  Should 
any  appreciable  residue  remain,  fuse  it  with  sodium  carbonate, 
dissolve  the  fusion  in  water  and  sulphuric  acid,  heat,  and  add 
to  the  main  filtrate.  To  the  combined  solutions,  which  should 
be  colorless  and  smell  strongly  of  sulphurous  acid,  add  a  clear 
filtered  solution  of  sodium  acetate  (20  gms.)  and  one  sixth  its 
volume  of  acetic  acid  (1.04  sp.  gr.),  heat  to  boiling,  and  con- 
tinue to  boil  for  a  few  minutes.  Allow  to  settle,  filter  on  an 
ashless  filter;  wash  thoroughly  with  hot  water  containing  17 
per  cent  acetic  acid,  and  finally  with  hot  water ;  dry,  ignite,  and 
weigh  as  TiO2.  This  precipitate  is  seldom  quite  pure,  as  it  is 
liable  to  contain  small  amounts  of  Fe3O3  and  A12O3.  Hence  it 
is  best  to  fuse  it  with  sodium  carbonate,  dissolve  in  water, 
filter,  wash,  dry,  and  fuse  the  insoluble  sodium  titanate  with 
sodium  carbonate,  dissolving  the  fusion,  when  cool,  in  the 
crucible  with  sulphuric  acid,  and  precipitate  and  determine 
the  TiO2  as  above. 

To  obtain  the  weight  of  titanium,  multiply  the  weight  of 
the  titanic  oxide  found  by  0.60976. 

Pig  Iron,  etc. — Decompose  according  to  Drown's  method 
for  the  determination  of  silicon  (Part  I,  Chapter  I,  page  85),, 
dry,  and  ignite  the  residue  of  silica,  graphite,  etc.  Treat  this 
residue  with  hydrofluoric  acid  and  sulphuric  acid  to  expel 
silica  and  evaporate  the  fumes  of  sulphuric  anhydride,  Finally, 
evaporate  to  dryness  and  fuse  with  sodium  carbonate.  Dis- 
solve the  fusion  in  water  and  sulphuric  acid,  heat,  and  add  the 
solution  to  the  main  filtrate.  Proceed  with  this  solution  as 
with  iron  ores. 


TITANIUM.  193 

Slags. — Treat  2  gms.  of  finely  pulverized  slag  in  a  large 
platinum  crucible  with  an  excess  of  hydrofluoric  acid  and  5  cc. 
of  cone,  sulphuric  acid.  Evaporate  off  the  hydrofluoric  acid, 
and  heat  carefully  until  the  greater  part  of  the  sulphuric  acid 
is  driven  off.  Allow  the  crucible  to  cool,  add  10  gms.  of 
sodium  carbonate,  fuse  for  half  an  hour,  finally  at  a  high  heat, 
and  remove  the  crucible,  running  the  fused  mass  well  up  on 
its  walls.  Dissolve  the  fused  mass  in  water,  transfer  to  a 
beaker,  and  filter.  Wash  the  insoluble  matter,  dry,  ignite,  and 
re-fuse  it  with  sodium  carbonate.  Dissolve  in  water  as  before,, 
and  filter.  By  this  method  alumina  will  be  entirely  separated 
from  the  titanium.  Fuse  the  insoluble  matter  on  the  filter 
with  spdium  carbonate,  dissolve  the  fusion,  when  cool,  with 
sulphuric  acid,  and  determine  the  titanium  as  above. 


CHAPTER   XX. 

MANGANESE   (Mn). 

A  NUMBER  of  methods  for  the  determination  of  manganese 
have  been  proposed,  and  a  number  of  different  methods  are  in 
use.  There  seems  to  be  considerable  difference  of  opinion 
between  many  of  our  best  chemists  as  to  which  are  the  best 
methods.  However,  the  methods  described  below  are  all  in 
use  in  some  of  our  largest  metallurgical  works  and  by  some  of 
our  most  reliable  technical  and  commercial  chemists. 

Ford's  Method.* — This  method  was  first  proposed  for  the 
determination  of  manganese  in  spiegels,  irons,  and  steels,  but 
is  applicable  to  slag,  ores,  etc.,  if  slightly  modified.  From  0.5 
to  2.0  grammes  of  substance,  depending  on  the  percentage  of 
manganese  it  contains,  are  dissolved  in  from  25  to  50  cc.  of 
strong  nitric  acid  (1.4  sp.  gr.)  perfectly  free  from  chlorine. 
Evaporation  to  dryness  is  not  necessary,  except  where  the 
amount  of  silicon  is  large,  as  in  the  case  of  certain  pig-irons. 
Then,  as  a  clogging  of  the  filter  in  the  subsequent  filtration  is 
apt  to  follow,  dissolve  first  in  a  dish  in  hydrochloric  acid,  using 
as  small  an  amount  of  acid  as  possible,  and  quickly  evaporate 
to  dryness.  Take  up  with  nitric  acid  and  evaporate  again  to 
dryness.  This  second  evaporation  is  necessary  in  order  to 
remove  all  the  hydrochloric  acid,  which,  if  present,  would 
interfere  with  the  subsequent  precipitation  of  the  manganese. 
Slag,  ores,  and  such  other  material  as  contains  much  silica, 
should  also  be  treated  in  this  way.  Redissolve  for  the  second 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  Vol.  IX, 
p.  397- 

1 04 


MANGANESE.  1 95 

time  in  strong  nitric  acid,  and  boil  until  the  red  fumes  cease 
coming  off,  and  while  boiling  throw  in  crystals  of  potassium 
chlorate  from  time  to  time.  Violent  action  ensues,  yellow 
fumes  are  driven  off,  and  binoxide  of  manganese  is  precipi- 
tated, since  it  is  insoluble  in  strong  nitric  acid.  As  soon  as 
all  of  the  manganese  has  been  oxidized  the  fumes  will  cease 
coming  off,  with  a  slight  explosion.  After  this  has  occurred, 
add  a  few  more  crystals  of  potassium  chlorate,  boil  for  a  min- 
ute or  two,  remove  from  the  lamp,  and  filter  through  an 
asbestos  filter.  The  most  convenient  apparatus  is  a  small 
funnel-shaped  tube  in  which  is  fitted  an  asbestos  plug,  the 
filter-pump  being  used  to  facilitate  filtration.  The  asbestos 
should  be  free  from  soluble  lime,  magnesia,  and  manganese. 
It  is  best  to  prepare  it  by  treating  it  successively  with  boiling 
hydrochloric  acid,  boiling  water,  boiling  nitric  acid,  and  then 
boiling  water  until  the  washings  no  longer  show  a  trace  of 
these  elements  when  treated  with  the  proper  reagents.  The 
asbestos  should  then  be  ignited  to  free  it  from  organic  matter. 
This  is  of  the  utmost  importance,  as  the  writer  has  known  of 
more  than  one  chemist  who  condemned  this  method  as  giving 
too  high  results,  when  upon  investigation  it  was  found  that 
they  had  not  taken  the  precaution  to  purify  the  asbestos  used, 
which  probably  accounted  for  the  high  results  obtained. 

After  filtering  the  nitric-acid  solution  through  the  asbestos 
filter,  rinse  the  dish  or  beaker  in  which  the  substance  was  dis- 
solved with  strong  nitric  acid,  pour  it  upon  the  filter,  and  wash 
with  strong  nitric  acid  until  the  washings  come  through  color- 
less. The  funnel-tube  is  then  removed  from  the  filtering  ap- 
paratus, the  filter  with  its  contents  placed  back  into  the  dish 
in  which  the  solution  was  made,  hydrochloric  acid  added,  and 
the  substance  boiled  until  the  manganese  binoxide  is  dissolved 
as  chloride.  The  asbestos  is  then  removed  by  filtration,  using 
the  same  tube  and  filter-pump,  and  finally  washing  with  hot 
water.  Nearly  neutralize  the  filtrate  with  ammonia,  adding  a 
few  crystals  of  sodium  acetate,  and  boil,  filter,  wash  slightly 
with  hot  water,  redissolve  the  small  precipitate  of  iron  oxide 
in  hydrochloric  acid,  again  nearly  neutralize  with  ammonia,  add 


A   MANUAL    OF  PRACTICAL  ASSAYING. 

a  crystal  or  so  of  sodium  acetate,  boil,  and  filter.  The  solution 
and  reprecipitation  of  the  iron  is  necessary  as  a  small  amount 
of  manganese  is  always  contained  in  the  first  precipitate.  Add 
the  second  filtrate  to  the  first,  heat  nearly  to  boiling,  and  add  an 
excess  of  microcosmic  salt.  Then  make  slightly  ammoniacal, 
and  boil,  stirring  until  the  precipitate  assumes  the  characteris- 
tic appearance  of  the  phosphate  of  ammonia  and  manganese. 
Allow  it  to  settle,  and  filter,  wash  with  hot  water,  dry,  ignite, 
and  weigh  as  pyrophosphate  of  manganese. 

It  is  best  to  use  some  filter-paper  which  is  pure,  such  as 
Schleicher  &  Schuell's  c.  p.,  for  both  filtrations,  as  many  of 
the  qualitative  papers  contain  appreciable  quantities  of  man- 
ganese. 

In  the  case  of  slags  or  other  substances  containing  lime 
and  magnesia,  it  is  necessary  to  wash  the  binoxide  precipitate 
more  thoroughly  with  nitric  acid  in  order  to  remove  all  of 
these  elements. 

Evaporation  to  dryness  in  the  case  of  steels  or  spiegels  is 
not  necessary.  They  may  be  immediately  dissolved  in  strong 
nitric  acid,  and  potassium  chlorate  added.  A  determination 
may  be  made  in  two  hours  by  this  method. 

Williams's  Method.* — Mr.  H.  Williams  has  proposed  a 
modification  of  the  above  method  which  shortens  it  somewhat, 
and  simplifies  it,  especially  in  the  case  of  a  substance  which 
contains  lime  or  magnesia,  as,  for  example,  slag. 

The  substance  is  treated,  as  before,  with  nitric  acid,  and 
potassium  chlorate  (in  the  case  of  a  pig-iron,  slag,  etc.,  the 
silica  and  carbon  must  first  be  removed  by  filtration  through 
asbestos)  added  to  precipitate  the  manganese.  After  filtering 
off  this  precipitated  manganese  binoxide,  wash  with  strong 
nitric  acid,  and  then  well  with  water.  Blow  the  contents  of 
the  funnel  into  the  beaker  in  which  the  precipitation  was 
made,  which  should  previously  be  well  washed,  and  rinse  the 
funnel  with  a  little  water. 


*  Transactions   of  the  American  Institute   of  Mining  Engineers,  Vol.  X, 
p.  loo. 


MANGANESE.  197 

Run  into  the  beaker  an  accurately  measured  quantity  of  a 
standard  solution  of  oxalic  acid  (a  moderate  excess  over  what 
the  manganese  binoxide  is  capable  of  oxidizing),  add  water  to 
bring  the  bulk  of  the  solution  up  to  about  75  cc.,and  then  3  or, 
4  cc.  of  concentrated  sulphuric  acid,  and  heat  to  about  70°  C. 
The  solution  of  the  binoxide  is  readily  effected  by  the  aid  of  a 
little  stirring.  Finally,  titrate  the  solution  with  a  standard  so- 
lution of  potassium  permanganate.  (See  Part  II,  Chapter  XVI.) 
The  presence  of  the  asbestos  does  not  obscure  the  final  reac- 
tion. Two  standard  solutions  are  necessary,  viz.,  a  permanga- 
nate solution  and  an  oxalic  solution. 

It  is  best  to  use  a  decinormal  permanganate  solution,  i.e., 
I  cubic  centimetre  equal  to  I  milligramme  of  iron.  By  using 
such  a  dilute  solution  the  accuracy  of  the  method  is  greatly 
increased.  The  permanganate  solution  may  be  prepared  by 
dissolving  1.2  grammes  of  potassium  permanganate  in  2030 
cc.  of  distilled  water.  It  should  be  prepared  and  standardized 
as  described  in  Part  II,  Chapter  XVI. 

The  oxalic  solution  may  be  of  almost  any  strength,  but  if 
it  is  made  so  that  I  cc.  will  require  about  3  cc.  of  the  perman- 
ganate solution  to  oxidize  it,  it  will  answer  well.  It  should  be 
kept  in  a  tight-stoppered  bottle  in  a  dark  place,  and  should 
be  standardized  from  to  time  with  the  standard  permanganate 
solution. 

The  method  of  calculating  the  result  is  best  shown  by  the 
following  example :  Suppose  we  have  taken  I  gramme  of  steel, 
in  which  we  suspect  about  I  per  cent  of  manganese.  Having 
separated  the  binoxide,  we  add  15  cc.  of  the  standard  oxalic- 
acid  solution  of  the  strength  already  mentioned,  and  effect  the 
the  solution  as  described.  This  15  cc.,  by  itself,  would  require 
45  cc.  of  the  permanganate,  but  on  titrating  we  use,  say,  25  cc.; 
the  difference,  20  cc.,  is  equivalent  to  0.020  gramme  of  iron. 
Since  I  equivalent  of  manganese  binoxide  converts  2  equiva- 
lents of  a  proto-salt  of  iron  to  the  state  of  a  sesqui-salt,  as 
shown  by  the  formula 

2FeSO4  +  MnO3  +  2HaSO4  =  Fea(SO4)3  +  MnSO4  +  2HaO, 


198  A    MANUAL    OF  PRACTICAL  ASSAYING. 

the  solving  of  the  proportion  112  :  55  ::  0.020  :  x  gives  the 
weight  of  the  manganese  equivalent  to  the  0.020  gramme  of 
iron.  The  value  of  x  is  0.00982  and  the  per  cent  is  0.982.  It 
will  be  seen  from  the  above  that  in  operating  on  ores  or  prod- 
ucts which  contain  a  high  percentage  of  manganese  it  will  be 
necessary  to  take  smaller  quantities  of  the  substance. 

Sometimes  when  the  percentage  of  manganese  is  high  it 
may  be  advantageous  to  use  a  stronger  solution  of  oxalic  acid 
and  also  a  stronger  solution  of  permanganate, — say  a  half- 
normal  solution. 

The  results  obtained  by  this  method  agree  very  closely  be- 
tween themselves,  and  also  with  the  results  obtained  by  Ford's 
method. 

The  following  modification  of  Ford's  method  the  writer  has 
used  for  the  determination  of  manganese  in  ores  and  slags  with 
very  good  results:  Dissolve  the  precipitated  binoxide  with 
just  sufficient  hydrochloric  acid  to  cause  the  precipitate  to  go 
into  solution,  and  add  a  little  sulphuric  acid.  An  emulsion  of 
pure  zinc  oxide  is  now  added,  a  little  at  a  time,  shaking  or 
stirring  the  solution  until  the  hydrochloric  acid  is  neutralized 
and  the  zinc  oxide  is  in  slight  excess.  Care  should  be  exer- 
cised not  to  add  too  large  an  excess  of  zinc  oxide,  as  if  too 
large  an  excess  is  present  it  will  obscure  the  reaction,  and  fil- 
tration will  be  necessary  before  the  solution  can  be  titrated. 
The  solution  is  now  ready  for  titration  with  standardized  per- 
manganate solution  in  the  manner  described  under  the  head  of 
Volhard's  Method. 

Volhard's  Volumetric  Method. — This  method,  which  is 
generally  used  in  the  Western  lead,  and  copper-smelting  works, 
may  be  used  for  the  determination  of  manganese  in  iron,  man- 
ganese, lead,  copper,  silver,  and  gold  ores,  etc.,  and  also  for  the 
determination  of  manganese  in  other  substances,  such  as  Spiegel, 
steel,  etc. 

Dissolve  I  gramme  of  substance  in  2  cc.  of  hydrochloric, 
4  cc.  of  nitric,  and  6  cc.  of  dilute  sulphuric  acids  in  a  flask  or 
casserole,  as  in  the  determination  of  iron,  and  evaporate  to 
copious  fumes  of  sulphuric  anhydride.  Transfer  the  contents  of 


MANGANESE.  199 

the  flask  or  casserole  to  a  graduated  500-00.  flask,  washing  into 
the  flask  with  boiling  water.  Then  add  an  emulsion  of  zinc 
oxide  to  the  contents  of  the  flask  until  the  acid  is  neutralized 
and  the  iron  is  all  precipitated  as  sesquioxide,  violent  shaking 
of  the  contents  of  the  flask  facilitating  the  precipitation  of  the 
iron.  After  the  precipitation  is  complete  the  oxide  of  zinc 
should  be  in  slight  excess.  The  contents  of  the  flask  are  then 
diluted  with  distilled  water  to  the  holding  mark,  and  after 
thorough  shaking  allowed  to  settle.  After  the  oxides  have 
settled  so  that  the  supernatant  liquid  is  comparatively  clear, 
100  cc.  is  drawn  off  by  means  of  a  pipette  and  transferred  to  a 
flask  (about  250  cc.  capacity),  rinsing  out  the  pipette  with  dis- 
tilled water  into  the  flask.  The  contents  of  the  small  flask  are 
then  brought  to  a  boil  by  heating  over  a  flame,  and  are  then 
ready  for  titration  with  a  standard  solution  of  permanganate 
of  potassium.  The  titration  is  performed  as  follows :  The  per- 
manganate solution  is  dropped  into  the  liquid  in  the  flask  from 
a  burette,  the  contents  of  the  flask  being  shaken  after  each  ad- 
dition of  permanganate  solution  in  order  to  facilitate  the  set- 
tling of  the  precipitated  manganese  dioxide.  From  the  amount 
of  the  precipitate  and  the  rapidity  with  which  the  precipitate 
is  formed  after  each  addition  of  permanganate  solution,  the 
operator  after  a  little  practice  will  be  able  to  determine  in 
what  quantities  it  is  safe  to  add  the  permanganate  solution. 
The  addition  of  permanganate  should  be  continued  until  a 
faint  pink  color  appears  around  the  edges  of  the  clear  liquid 
after  shaking,  when  held  against  a  white  background.  The 
precipitation  of  the  manganese  is  then  complete,  although  it  is 
safest,  especially  if  the  precipitation  has  occupied  some  time,  to 
bring  the  contents  of  the  flask  again  to  a  boil,  and  notice,  after 
allowing  the  precipitate  to  settle,  if  the  pink  tint  remains.  If 
the  color  should  have  disappeared  another  drop  of  permanga- 
nate is  added,  the  flask  shaken,  and  the  precipitate  allowed  to 
settle.  If  the  color  is  permanent  after  settling  the  titration  is 
completed. 

The  same  solution  of  potassium  permanganate  used  for  the 
determination  of  iron  may  be  used  for  this  determination.     In 


200  A   MANUAL    OF  PRACTICAL   ASSAYING. 

order  to  determine  how  much  manganese  one  cubic  centimetre 
of  the  permanganate  solution  is  equal  to,  it  is  only  necessary 
to  multiply  its  value  for  iron  by  0.2946  to  obtain  its  value  for 
manganese.  Hence  if  the  I  cc.  of  the  permanganate  solution 
was  equal  to  o.oio  gramme  of  iron,  it  would  be  equal  to 
0.002946  gramme  of  manganese.  The  reaction  which  takes 
place  is  as  follows :  3MnO  +  Mn3O7  =  5MnO2. 

Many  chemists  prefer  to  filter  off  the  precipitated  oxides 
before  diluting  to  500  cc. ;  but  this  is  unnecessary,  as  the  pre- 
cipitate occupies  such  a  small  bulk,  although  in  the  flocculent 
state  its  bulk  appears  to  be  large,  that  it  may  be  disregarded. 
Moreover,  the  precipitate  is  difficult  to  wash,  and  filtration 
generally  gives  low  results.  The  method  gives  closely  agree- 
ing results,  and  results  which  are  as  good  as  if  not  better  than 
those  obtained  by  the  other  methods  with  the  same  degree 
of  proficiency  in  practice.  The  zinc  oxide  should  be  tested, 
and,  if  it  contains  manganese  or  organic  matter,  purified.  If 
commercial  zinc  is  used  it  will  be  necessary  to  purify  it. 

Colorimetric  Method. — This  method  was  first  used  in 
this  country  by  Mr.  Samuel  Peters,*  and  is  especially  appli- 
cable to  the  estimation  of  manganese  in  steels,  and  such 
substances  as  contain  less  than  I J  to  2  per  cent  of  manganese. 
The  method,  as  used  in  iron  and  steel  laboratories,  is  essentially 
as  follows,  for  steels:  Dissolve  o.i  gramme  of  the  steel  in  20 
cc.  nitric  acid  (1.20  sp.  gr.)  in  a  test-tube  about  nine  inches 
long  by  one  inch  in  diameter,  by  the  aid  of  heat,  boiling  the 
solution  until  the  carbonaceous  matter  is  entirely  in  solution 
and  all  nitrous  fumes  are  evolved.  This  usually  takes  about 
five  minutes  at  a  gentle  ebullition.  Then  add,  with  a  platinum 
spatula,  about  0.4  gramme  of  pure  peroxide  of  lead  to  the 
boiling  solution,  adding  first  a  small  portion  of  the  lead,  and 
as  soon  as  the  violent  action  ceases,  an  instant  later,  the 
remainder  of  the  salt,  boiling  gently  but  continuously  for 
exactly  two  and  a  half  minutes  longer,  then  removing  from 


*  Crooks'  Select  Methods.    Transactions  of  the  American  Institute  of  Mining 
Engineers,  Vol.  XV,  p.  104. 


MANGANESE.  2O1 

the  heat,  and  placing  the  test-tube  in  a  beaker  of  cold  water, 
out  of  contact  with  the  direct  rays  of  sunlight,  and  allowing 
the  solution  to  cool  and  to  settle  for  about  an  hour.  The 
clear  supernatant  solution  is  then  ready  to  decant  off  from  the 
lead  into  the  graduated  tube,  and  to  match,  by  dilution  with 
distilled  water,  with  the  standard  solution  containing  o.oooi 
gramme  of  manganese  as  permanganate  in  each  cc.  of  solu- 
tion;  so  that,  using  O.I  gramme  of  steel  for  the  analysis,  each 
cc.  of  the  solution  to  be  determined  will  represent  o.oi  per 
cent  of  manganese  when  the  shades  of  color  match. 

The  standard  solution  for  comparison  may  be  made  in 
several  ways,  but  the  best  are  to  use  either  a  standard  solution 
of  potassium  permanganate  or,  preferably,  the  standard  may 
be  prepared  by  using  o.i  gramme  of  a  standard  steel  contain- 
ing a  known  percentage  of  manganese,  treating  it  exactly  as 
the  unknown  sample,  and  decanting  the  solution  into  a  simi- 
larly graduated  tube,  and  diluting  with  water  until  the  solution 
has  a  volume  of  which  the  number  of  cc.  is  an  equivalent  or 
multiple  of  the  percentage  of  manganese  in  the  steel,  applying 
the  same  principle  as  is  used  with  the  standard  steels  in  the 
Eggertz  method  for  the  estimation  of  carbon  (see  Part  II, 
Chapter  IV).  This  method  is  preferable  to  the  other  methods 
of  making  a  comparison,  and  it  is  also  preferable  to  run  a 
standard  with  each  set  of  analyses. 

A.  E.  Hunt*  says:  "This  method,  when  properly  used,  is 
at  least  sufficiently  accurate  for  all  practicable  purposes  within, 
say,  0.02  per  cent  manganese  for  steels  within  the  range  of  from 
0.15  to  1.50  per  cent  manganese.  It  is  fully  as  accurate,  and 
can  be  as  safely  guarded  from  error,  as  the  Eggertz  color-method 
for  the  estimation  of  carbon  in  steel."  The  method,  however, 
has  many  sources  of  error  that  must  be  carefully  avoided. 

Mr.  Hunt  recommends  the  following  precautions : 

First.  The  drillings  of  steel  must  have  no  oil  or  other 
extraneous  matter  with  them.  Owing  to  the  ease  with  which 


*  Transactions  of  the  American  Institute  of  Mining  Engineers,  Vol.  XV, 
p.  106. 


> 

/ 


2O2  A    MANUAL   OF  PRACTICAL   ASSAYING. 

permanganate  solutions  are  reduced,  it  is  necessary  that  no 
organic  matter  be  present  which  will  not  be  entirely  destroyed 
by  the  boiling  nitric  acid  before  the  addition  of  the  peroxide 
of  lead. 

Second.  The  nitric  acid  must  be  pure,  and  especially  free 
from  chlorine  or  nitrous  fumes.  The  acid  must  be  of  very 
nearly  i.2Osp.  gr.  throughout  the  process,  and  must  not  be  al- 
lowed to  become  much  more  concentrated  by  boiling.  It  is 
best  to  cover  the  mouths  of  the  test-tubes  with  clean  covers 
of  porcelain  crucibles  during  the  ebullition.  If  the  acid  be- 
comes too  concentrated  during  the  boiling,  as  it  is  very  liable 
to  do  if  the  ebullition  becomes  too  violent  and  the  test-tube  is 
a  large  one,  on  the  addition  of  the  peroxide  of  lead  some  of 
the  manganese  is  transformed  into  the  insoluble  manganese 
binoxide  and  precipitated. 

Third.  The  peroxide  of  lead  must  be  free  from  color  on 
boiling  with  the  dilute  nitric  acid,  and  must  be  so  free  from 
lead  nitrate  that  it  will  oxidize  all  the  manganese  in  the  steel 
into  a  reasonably  permanent  permanganic  acid.  This  is  a  very 
important  point,  which,  not  properly  guarded,  has  occasioned 
failures,  and  has -caused  many  chemists  to  condemn  the  method. 
In  commencing  the  use  of  any  new  lot  of  peroxide  of  lead 
it  is  a  necessary  precaution  to  mix  up  the  salt  thoroughly 
and  then  to  test  it  by  making  an  analysis  with  a  steel  of  known 
composition,  comparing  it  with  a  standard  solution  of  potassium 
permanganate,  and  obtaining  a  concordant  result.  Most  of  the 
peroxide  of  lead  found  in  the  markets  and  sold  as  c.  p.  is  non- 
homogeneous,  and  contains  considerable  quantities  of  nitrate 
disseminated  through  it.  It  is  best  to  purify  your  own  perox- 
ide of  lead. 

Fourth.  The  ebullition  must  not  be  too  violent,  and  must 
not  last  over  two  and  one  half  minutes.  It  is  necessary  to 
stand  by  the  tubes  with  watch  in  hand  and  to  remove  them 
when  the  time  is  up.  Too  long  boiling  invariably  gives  bad 
results.  The  boiling  is  best  done  in  a  water-bath  in  which 
chloride  of  calcium  is  added  to  the  water  to  raise  its  boiling- 
point. 


.      MANGANESE.  2O3 

Fifth.  There  must  not  be  hydrochloric  acid,  sulphuretted 
hydrogen,  or  other  fumes  in  the  air  of  the  room  in  which  the 
tubes  are  allowed  to  stand  to  cool.  It  is  best  not  to  allow  the 
solution  to  stand  too  long — never  two  hours — before  com- 
parison. 

Sixth.  Mr.  Hunt  says:  "I  have  had  no  trouble  in  getting 
good,  reasonably  permanent  colors,  but  have  never  had  uni- 
formly satisfactory  results  by  filtering  the  solution  from  the 
peroxides  through  asbestos,  and  have  consequently  preferred 
to  decant  off  the  solution  from  the  lead.  When  a  standard 
steel  is  used,  having  nearly  the  same  percentage  of  manganese 
as  the  sample  to  be  determined,  equal  amounts  of  solution  and 
treatment  exactly  the  same  so  far  as  practicable,  the  error  due 
to  the  amount  of  the  liquid  remaining  with  the  lead  in  the  bot- 
tom of  the  tube  is  comparatively  trifling,  never  over  0.02  per 
cent,  when  the  precautions  mentioned  above  are  carefully  ob- 
served." 

Seventh.  The  water  used  in  diluting  must  be  free  from 
organic  matter.  The  ordinary  distilled  water  used  in  chemi- 
cal laboratories  often  contains  considerable  organic  matter, 
which  will  rapidly  reduce  the  permanganate  solution. 

Eighth.  The  mixing  of  the  color  solutions  for  comparison 
can  best  be  done  by  having  the  graduated  tube  provided  with 
a  glass  stop-cock,  or  it  can  be  satisfactorily  performed  by  pour- 
ing the  solution  out  into  a  clean  beaker  and  then  decanting 
back  into  the  graduated  tube. 

This  method  is  especially  applicable,  owing  to  its  simplic- 
ity and  rapidity,  for  checking  and  controlling  the  converting 
and  mill  work  in  a  steel-works.  When  great  rapidity  is  neces- 
sary, as  it  sometimes  may  be  in  this  latter  case,  the  solution 
need  not  be  allowed  to  stand  so  long  after  the  addition  of  the 
peroxide  of  lead,  but  may  be  filtered  through  asbestos,  using 
the  filter-pump. 

The  above  methods  will  serve  for  the  estimation  of  man- 
ganese in  almost  any  substance.  Volhard's  method  is  the  one 
generally  used  in  the  West,  and  is  the  simplest  and  most  rapid. 
In  the  case  of  oxidized  ores,  soluble  in  hydrochloric  acid,  the 


204  A   MANUAL   OF  PRACTICAL  ASSAYING. 

addition  of  nitric  and  sulphuric  acids  may  be  dispensed  with, 
the  ore  being  dissolved  directly  in  a  small  quantity  of  hydro- 
chloric acid,  and  the  manganese  determined  by  Volhard's 
method  as  above.  In  the  case  of  slags,  when  the  sample  has 
been  suddenly  chilled  (Chapter  I),  treat  with  water  and  hydro- 
chloric acid,  as  in  the  determination  of  silica,  add  a  few  crystals 
of  potassium  chlorate,  heat  to  oxidize  the  iron,  etc.,  and  deter- 
mine by  Volhard's  method.  When  the  sample  has  not  been 
suddenly  chilled,  make  a  cintering  fusion  (Chapter  I),  dissolve 
fused  mass  as  above,  evaporate  to  dryness  and  heat.  Redis- 
solve  in  hydrochloric  acid,  and  proceed  by  Volhard's  method. 

Mr.  A.  H.  Low*  proposes  a  method  for  the  determination 
of  manganese  in  ores  which  is  a  combination  of  Volhard's  and 
William's  methods,  and  which  is  said  to  give  excellent  results. 

The  method  is  essentially  as  follows;  Dissolve  0.5  gm.  of 
ore  in  hydrochloric  acid,  or  nitrohydrochloric  acids,  in  a  flask. 
Heat  until  most  of  the  free  acid  is  expelled,  dilute  with  75  cc. 
of  water,  add  an  excess  of  zinc  oxide,  and  boil.  Now  add  a 
saturated  solution  of  bromine-water  (not  over  50  cc.),  and  boil 
out  the  excess  of  bromine.  The  solution  should  still  contain 
an  excess  of  zinc  oxide.  Filter,  and  wash  the  precipitate  thor- 
oughly with  hot  water.  Return  the  washed  precipitate  to  the 
flask  and  add  50  cc.  of  dilute  sulphuric  acid  (i  in  9).  Warm 
to  dissolve  the  iron,  and  run  in  an  excess  of  oxalic-acid  solution 
from  a  burette,  heat,  dilute  with  warm  water,  and  titrate  the 
excess  of  oxalic  acid  with  a  standard  solution  of  potassium 
permanganate. 

The  permanganate  solution  should  be  about  one-tenth  nor- 
mal. The  oxalic-acid  solution  is  prepared  by  dissolving  11.46 
gms.  of  pure  crystallized  oxalic  acid  in  1000  cc.  of  water.  The 
solutions yare  standardized  in  the  usual  manner,  and  their  rela- 
tions to  each  other  determined. 

*Journal  of  Analytical  and  Applied  Chemistry,  Vol.  VI,  p.  663. 


CHAPTER  XXL 
ZINC   (Zn). 

SEVERAL  methods  have  been  proposed  for  the  determination 
of  zinc  both  gravimetrically  and  volumetrically.  Only  one, 
the  volumetric  estimation  by  a  standard  solution  of  potassium 
ferrocyanide,  will  be  given.  For  the  standard  gravimetric 
methods  see  Fresenius,  Cairns,  Rose,  etc. 

This  method,  provided  the  proper  precautions  are  used, 
gives  results  which  agree  as  closely  with  the  results  obtained  by 
any  of  the  standard  gravimetric  methods  as  two  gravimetric 
determinations  of  the  same  sample  will  agree  among  them- 
selves, provided  the  percentage  of  zinc  present  is  not  very  low 
(less  than  4  per  cent).  The  accuracy  of  the  method  has  been 
fully  demonstrated.  See  Proceedings  of  the  Colorado  Scien- 
tific Society,  June  1892,  and  The  School  of  Mines  Quarterly, 
Vol.  XIV,  No.  i,  p.  40. 

It  is  the  opinion  of  the  writer,  after  numerous  experiments, 
that  once  the  zinc  is  obtained  in  solution  in  the  proper  form 
its  percentage  may  be  more  safely  determined  by  this  titra- 
tion  method  than  it  can  be  by  precipitation  and  subsequent 
ignition  and  weighing.  It,  moreover,  has  the  advantage  of 
being  rapid,  and  consequently  would  be  used  in  metallurgical 
works  in  many  instances,  even  if  the  results  were  not  quite  up 
to  the  standard  of  accuracy. 

This  method  requires  a  standard  solution  of  potassium 
ferrocyanide.  A  solution  of  which  one  cubic  centimetre  is 
equal  to  o.oio  gramme  of  zinc  is  the  solution  generally  pre- 
ferred by  most  chemists  using  this  method.  To  prepare  such 
a  solution  90  grammes  of  pure  potassium  ferrocyanide  (free  from 

205 


2O6  A    MANUAL    OF  PRACTICAL   ASSAYING. 

potassium  ferricyanide)  are  dissolved  in  two  litres  of  water  and 
kept  in  a  tightly-stoppered  green-glass  bottle.  The  solution 
will  keep  for  some  time  without  alteration,  provided  the  bottle 
is  well  stoppered,  and  need  not  be  tested  more  frequently  than 
once  every  two  or  three  weeks.  It  is  best  to  make  up  the  solu- 
tion at  least  one  day  before  using.  To  standardize  the  solution, 
dissolve  two  portions  of  about  0.250  gramme  each  of  pure  zinc 
oxide  (the  zinc  oxide  should  previously  be  ignited  to  convert 
any  carbonate  of  zinc  into  oxide,  and  kept  in  a  stoppered 
bottle  so  that  it  may  not  absorb  carbonic  acid  or  water  from  the 
air)  in  5  cc.  of  pure  hydrochloric  acid,  and  add  50  cc.  of  water 
in  a  beaker  of  about  300  cc.  capacity.  In  order  to  have  the 
same  conditions  present  as  near  as  possible  as  in  the  actual 
analysis,  it  is  well  to  add  ammonia  in  slight  excess  and  then 
neutralize  with  hydrochloric  acid,  using  a  small  piece  of  litmus- 
paper  as  an  indicator.  When  the  solution  has  been  brought 
to  the  point  where  it  is  just  slightly  acid,  add  an  excess  of  10  cc. 
of  pure  strong  hydrochloric  acid,  and  dilute  to  250  cc.  with 
cold  distilled  water.  The  solution  is  now  ready  for  titration 
with  the  ferrocyanide  solution,  which  may  be  run  in  from  a 
burette,  rapidly  at  first,  stirring  from  time  to  time.  If  0.2493 
gramme  of  pure  oxide  of  zinc  were  weighed  out,  it  would  require 
just  19.99  cc.  or  practically  20  cc.  of  the  ferrocyanide  solution  to 
precipitate  the  zinc,  provided  the  solution  was  normal ;  hence 
in  this  case  about  18  cc.  may  be  run  in  before  testing.  In 
order  to  test,  the  solution  is  thoroughly  stirred  with  a  glass  rod, 
and  a  drop  removed  and  added  to  a  drop  of  a  solution  of  pure 
uranium  acetate  on  a  porcelain  plate.  The  uranium-acetate 
solution  is  prepared  by  dissolving  sufficient  uranium  acetate  in 
water  to  give  a  pretty  strong  solution,  and  clarified  by  adding 
a  few  drops  of  acetic  acid.  This  solution  should  be  kept  in  a 
small  stoppered  bottle  in  a  dark  place,  as  it  is  decomposed  by 
the  action  of  sunlight.  As  long  as  there  is  not  an  excess  of  fer- 
rocyanide in  the  solution  the  drop  of  uranium  acetate  will  retain 
its  yellow  color ;  as  soon  as  the  ferrocyanide  is  in  slight  excess 
it  will  turn  a  light  brown,  the  shade  being  darker  according  to 
the  amount  of  ferrocyanide  in  excess.  The  titration  should  be 


ZINC.  207 

proceeded  with,  testing  after  the  addition  of  each  drop  of 
ferrocyanide  towards  the  last  of  the  operation,  and  stirring  well 
before  testing,  until  a  slight  brownish  tint  is  produced  on  the 
drop  of  uranium  acetate.  The  amount  of  ferrocyanide  used  is 
then  noted,  and  the  value  of  one  cubic  centimetre  calculated. 
The  duplicates  should  not  differ  by  more  than  one  tenth  of  a 
cubic  centimetre. 

The  precautions  to  be  observed  are  :  to  have  about  the  same 
bulk  of  solution  in  all  subsequent  titrations ;  to  have  the  same 
amount  of  hydrochloric  acid  present ;  to  have  the  standard 
solution  at  about  the  same  temperature,  and  to  have  the  zinc 
solution  comparatively  cool.  If  too  large  an  excess  of  acid  is 
present,  or  if  the  zinc  solution  is  too  warm,  a  decomposition  will 
ensue,  resulting  in  the  liberation  of  chlorine.  This  may  be 
seen  by  the  solution  turning  yellow  or  a  yellowish  green.  The 
precipitate  should  always  be  white,  and  the  solution  colorless 
or  nearly  so.  This  method  is  due  to  Fahlberg. 

To  determine  the  zinc  in  an  ore  by  this  method,  the  zinc 
solution  must  first  be  freed  from  such  elements  as  copper,  iron, 
manganese,  etc.,  which  are  also  precipitated  in  an  acid  solution 
with  the  ferrocyanide,  or  react  on  it.  The  three  elements 
named  above  are  the  ones  most  likely  to  be  encountered  in 
zinc  ores.  Should  cadmium  be  present  (its  presence  in  ores  of 
zinc  is  rare)  it  must  be  removed  before  proceeding  with  the 
titration. 

The  following  method  will  serve  for  the  determination  of 
zinc  in  all  ores  and  furnace-products,  except  in  the  special  cases 
mentioned  below. 

Method  of  Von  Schulz  and  Low  modified.*— Treat  i 
gm.  of  finely  pulverized  ore  with  15  cc.  of  aqua  regia,  and 
evaporate  nearly  to  dryness.  Should  the  ore  be  incompletely 
decomposed,  which  will  seldom  happen,  evaporation  to  dryness, 
dehydration  of  the  silicic  acid,  and  fusion  of  the  insoluble  res- 


*  The  Mining  Industry,  Denver,  Colo.,  Vol.  VI,  No.  13  ;  Proceedings  of 
the  Colorado  Scientific  Society,  June  1892  ;  School  of  Mines  Quarterly,  Vol. 
XIV,  No.  i. 


208  A    MANUAL    OF  PRACTICAL  ASSAYING. 

idue  with  carbonate  and  nitrate  of  soda,  after  solution  and 
filtration  of  the  silica,  will  be  necessary.  In  this  case  the  first 
and  second  filtrates  are  combined,  nitric  acid  is  added,  and  the 
solution  is  evaporated  nearly  to  dryness.  To  the  ore  or  nearly 
dry  mass  add  25  cc.  of  a  solution  of  potassium  chlorate  in 
nitric  acid,  prepared  by  shaking  an  excess  of  the  crystals  with 
strong  pure  nitric  acid  in  a  flask.  Add  the  solution  gradually 
and  do  not  cover  at  first,  but  warm  gently  until  all  violent 
action  has  stopped  and  greenish  fumes  cease  coming  off.  Then 
cover  with  a  watch-glass  and  boil  on  a  hot  iron  plate  to  dryness, 
— overheating  or  baking  should  be  avoided, — a  drop  of  nitric 
acid  adhering  to  the  cover  doing  harm.  Cool  sufficiently  and 
add  7  gms.  of  ammonium  chloride,  15  cc.  of  strong  ammonia- 
water,  and  25  cc.  of  hot  water.  Replace  the  cover  on  the 
casserole  and  boil  for  one  minute,  stirring  with  a  rubber-tipped 
glass  rod  to  break  up  all  particles  or  clots  of  solid  matter  on 
the  sides  and  bottom  of  the  casserole  and  the  cover.  Filter 
into  a  flask  of  about  250  cc.  capacity,  and  wash  several  times 
with  a  hot  solution  of  ammonium  chloride  prepared  as  follows: 
Dissolve  10  gms.  of  ammonium  chloride  in  1000  cc.  of  water, 
and  before  using  heat  to  boiling  in  a  wash-bottle  and  render 
slightly  alkaline  with  ammonia.  Should  a  considerable  pre- 
cipitate be  produced  it  will  carry  down  zinc  hydrate  with  it. 
In  the  case  of  a  small  precipitate  the  amount  of  zinc  which  it 
retains  may  be  disregarded.  If  a  large  precipitate  forms  it 
should  be  transferred  from  the  filter  to  the  original  decom- 
posing vessel  by  means  of  a  spatul,  and  wash-bottle,  using  as 
little  water  as  possible.  The  excess  of  water  is  evaporated  off 
and  the  precipitate  finally  treated  with  the  mixture  of  chlorate 
and  nitric  acid  as  before.  The  second  precipitate  is  treated 
with  ammonia,  ammonium  chloride,  and  water,  filtered  and 
washed  as  before,  the  second  alkaline  filtrate  being  combined 
with  the  first.  A  blue  coloration  in  the  filtrate  indicates  the 
presence  of  copper,  which  must  be  removed  before  proceed- 
ing with  the  titration.  Add  hydrochloric  acid  to  neutralization 
(indicated  by  the  gradual  disappearance  of  the  blue  color),  and 
then  10  cc.  of  hydrochloric  acid  in  excess.  If  the  solution  is 


ZfNC.  2O9 

not  sufficiently  warm  (about  70°  C.)  it  should  now  be  heated 
to  that  point.  Now  add  from  20  to  40  gms.  of  test-lead  and 
shake  vigorously  until  all  the  copper  is  precipitated.  The 
amount  of  test-lead  and  the  amount  of  shaking  necessary  will 
of  course  depend  upon  the  amount  of  copper  present,  which 
will  be  indicated  by  the  depth  of  the  blue  color  before  neutral- 
ization. Aluminium-foil  may  be  used  for  the  precipitation  of 
the  copper  in  place  of  test-lead.  In  case  aluminium  is  used  it 
should  be  cut  into  strips  of  a  convenient  size,  the  strips  being 
removed  and  washed  after  the  copper  is  all  precipitated.  The 
copper  can  be  removed  from  the  foil  when  it  is  ready  for  use 
again,  it  being  serviceable  until  it  becomes  too  thin  for  further 
use.  If  test-lead  is  used  it  is  best  to  use  fresh  lead  for  each 
determination.  In  case  copper  is  absent  the  above  treat- 
ment with  test-lead  or  aluminium  may  be  dispensed  with.  In 
this  latter  case  it  is  best  to  add  a  piece  of  litmus-paper,  two 
drops  of  methyl  orange,  or  some  suitable  indicator  to  the 
alkaline  solution,  then  hydrochloric  acid  until  the  solution  is 
neutral,  and  finally  an  excess  of  10  cc.  of  acid.  The  solution  is 
now  ready  for  the  determination  of  the  zinc  with  the  standard 
solution  of  potassium  ferrocyanide,  as  described  above  in 
standardization  of  the  solution.  A  very  good  plan  in  titrating, 
when  the  per  cent  of  zinc  is  not  approximately  known,  is  to 
pour  off  about  half  of  the  solution  into  a  beaker  and  titrate 
roughly.  This  will  give  the  approximate  per  cent  of  zinc, 
when  the  balance  of  the  fluid  in  the  flask  is  added  to  the  con- 
tents of  the  beaker  and  the  titration  proceeded  with,  a  con- 
siderable, or  such,  quantity  of  the  standard  solution  being 
added  as  the  per  cent  of  zinc,  as  approximately  determined, 
will  allow.  The  flask  is  finally  thoroughly  rinsed  out  with 
water,  the  rinsings  being  added  to  the  beaker,  and  the  titration 
finished  by  adding  a  few  drops  of  the  standard  solution  at  a 
time,  testing  a  drop  of  the  solution,  after  each  addition,  with  the 
uranium-acetate  solution.  At  the  first  indication  of  a  brown 
color  the  addition  of  the  ferrocyanide  is  stopped  and  the  read- 
ing of  the  burette  taken.  If  we  have  approximately  the  same 
bulk  of  solution  and  the  same  amount  of  free  acid  present  in 


2IO  A   MANUAL   OF  PRACTICAL  ASSAYING. 

the  regular  assay  as  we  have  in  the  standardization  of  the 
ferrocyanide  solution,  no  allowance  need  be  made  for  the 
quantity  of  excess  of  ferrocyanide  (about  two  drops)  necessary 
to  color  the  indicator. 

Slags. — In  the  case  of  slags  it  is  necessary  to  evaporate 
the  solution  of  the  slag  (if  the  sample  is  obtained  by  sudden 
chilling,  the  acid  solution;  or,  if  fusion  was  necessary  to  decom- 
pose the  slag,  the  solution  of  the  fusion)  to  dryness,  heat  to 
dehydrate  the  silicic  acid,  and  finally  dissolve  the  dry  mass  in  a 
little  water  and  nitric  acid.  Now  add  the  chlorate  mixture 
and  proceed  as  above.  Unless  this  precaution  be  taken  the 
results  will  invariably  be  low,  probably  owing  to  the  gelatinous 
silica  retaining  a  portion  of  the  zinc  solution. 

Ores  containing  Cadmium. — The  acid  solution,  before 
adding  test-lead  or  aluminium,  is  subjected  to  the  passage  of  a 
rapid  current  of  sulphuretted  hydrogen.  This  precipitates  the 
cadmium  as  well  as  the  copper.  When  the  precipitation  is 
complete  the  sulphide  precipitate  is  filtered  off  and  washed, 
when  the  filtrate  is  ready  for  titration  as  before,  it  being  un- 
necessary to  expel  the  excess  of  sulphuretted  hydrogen  by 
boiling  before  proceeding  with  the  titration. 

With  many  ores,  especially  the  sulphide  ores  of  the  west, 
treatment  with  aqua  regia  is  unnecessary  in  order  to  effect 
complete  decomposition,  simple  treatment  with  the  nitric-acid 
potassium-chlorate  mixture  being  sufficient. 

A  determination,  except  when  a  fusion  is  necessary  to 
effect  decomposition,  or  cadmium  is  present,  may  be  made  in 
30  minutes. 

Manganiferous  Ores.— Mr.  G.  C.  Stone*  proposes  a  modi- 
fication of  the  Von  Schulz  and  Low  method  which  presents 
some  advantages,  especially  in  the  analysis  of  zinc-manganese 
ores,  such  as  the  New  Jersey  ores. 

The  method  is  essentially  as  follows  : 

Sulphide  ores  are  best  dissolved  in  hydrochloric  acid  and  po- 
tassium chlorate,  care  being  taken  to  have  sufficient  acid  present 

*  Journal  Am.  Chem.  Society,  Vol.  XVII,  page  473,  June  1895. 


ZINC.  2lOa 

to  insure  keeping  all  the  manganese  in  solution.  Oxides,  car- 
bonates, and  silicates  are  dissolved  in  hydrochloric  acid  and 
oxidized  by  boiling  with  potassium  chlorate.  Ores  containing 
franklinite  or  rhodonite  must  be  first  fused  with  sodium  car- 
bonate and  evaporated  to  dryness  with  hydrochloric  acid  to 
thoroughly  decompose  them  ;  then  taken  up  with  hydrochloric 
acid  in  slight  excess  and  boiled  with  potassium  chlorate  to  in- 
sure oxidation  of  the  iron.  The  iron  and  alumina  are  removed 
by  precipitating  with  barium  carbonate.  The  barium-carbonate 
solution  is  prepared  by  treating  a  pure  salt,  free  from  ammo- 
nium salts  (as  Merk's),  by  suspending  in  water,  warming  for 
several  hours  with  two  or  three  per  cent  of  its  weight  of 
barium  chloride ;  this  converts  the  alkaline  carbonate  present 
into  chloride  and  the  small  excess  of  soluble  barium  salt  present 
does  not  interfere. 

The  thoroughly  oxidized  solution  of  the  ore  is  washed  into 
a  5OO-CC.  flask,  cooled,  and  barium  carbonate,  suspended  in 
water,  added  until  the  precipitate  curdles,  an  excess  doing  no 
harm.  Fill  to  the  5oocc.  mark,  pour  into  a  beaker,  mix  thor- 
oughly, allow  to  settle,  decant  the  clear  liquid  through  a  dry 
filter,  and  take  aliquot  portions  for  titration. 

The  solution  should  be  filtered  from  the  iron  at  once  (to  avoid 
precipitation  of  zinc)  and  should  be  titrated  as  soon  as  filtered. 
The  titration  for  manganese  is  performed  by  standard  potassium 
permanganate  solution  (see  page  198),  the  result  being  the  per- 
centage of  manganese  as  calculated  from  the  weight  of  ore 
taken. 

In  a  second  portion,  made  slightly  acid  with  hydrochloric 
acid,  the  zinc  and  manganese  are  titrated  together  by  standard 
potassium-ferrocyanide  solution.  As  manganese  ferrocyanide 
is  soluble  in  a  large  excess  of  hydrochloric  acid,  a  considerable 
excess  should  be  avoided.  Five  cc.  added  to  100  cc.  of  the 
solution  does  not  cause  any  appreciable  error;  larger  quantities 
are  to  be  avoided.  The  titration  is  performed  as  described 
(page  209),  except  that  a  quite  dilute  solution  of  cobalt  nitrate  is 
used  as  an  indicator  in  place  of  the  uranium  salt.  A  drop  of  the 
cobalt  solution  is  placed  on  a  white  porcelain  plate,  and  a  drop 


2lQb  A   MANUAL   OF  PRACTICAL  ASSAYING. 

of  the  solution  to  be  tested  is  added  so  that  the  drops  touch, 
but  do  not  mix ;  an  immediately  shown  greenish  line  at  the 
junction  of  the  drops  marks  the  end  reaction.  The  solution 
should  be  cold — not  warmer  than  the  ordinary  temperature  of 
the  laboratory. 

The  manganese  is  precipitated  as  Mn3Fe3(CN)12 ;  hence  an 
amount  of  ferrocyanide  that  will  precipitate  four  atoms  of  zinc 
will  only  precipitate  three  atoms  of  manganese. 

The  calculation  of  results  is  best  illustrated  by  an  example  : 
The  strength  of  the  ferrocyanide  solution  was  I  cc.  —  0.00606 
gm.  zinc.  The  strength  of  the  permanganate  solution  was  I  cc. 
=  o.ooi  gm.  manganese:  2.$  gms.  of  ore  were  dissolved  and 
the  solution  was  diluted  to  500  cc. ;  50  cc.  of  this  solution  was 
taken  for  the  determination  of  manganese  and  100  cc.  for  the 
determination  of  zinc.  As  18.45  cc-  (—  7-3^  Per  cent  Mn)  was 
used  in  the  first  and  27.85  cc.  was  used  in  the  second  titration, 
it  is  necessary  to  deduct  9.61  cc.  (for  the  0.0369  gm.  of  Mn 
present  in  the  100  cc.)  from  27.85  cc.,  leaving  18.24  cc.  for  the 
zinc,  equal  to  0.11053  gm.,  or  22.11  per  cent  zinc. 


CHAPTER   XXII. 
NICKEL  (Ni)AND   COBALT   (Co). 

NICKEL  and  cobalt  are  almost  invariably  associated  with 
each  other  in  ores  and  metallurgical  products,  and  consequently 
a  determination  of  either  metal  generally  involves  their  separa- 
tion. A  number  of  different  methods  for  the  separation  and 
determination  of  nickel  and  cobalt  have  been  proposed,  but 
the  writer  believes  the  following  to  be  as  rapid  and  accurate  as 
any :  . 

The  material  should  first  be  examined  for  members  of  the 
sulphuretted-hydrogen  group.  If  any  members  of  this  group 
are  found  to  be  present,  it  will  be  necessary  to  remove  them 
before  proceeding  with  the  analysis.  To  remove  the  members 
of  the  sulphuretted-hydrogen  group  dilute  the  filtrate  from 
the  silica  with  water  to  about  60  cc.,  warm  to  about  70°  C,  and 
pass  a  rapid  current  of  sulphuretted-hydrogen  gas,  allowing  the 
solution  to  cool  during  the  passage  of  the  gas.  Filter  out  the 
precipitated  sulphides,  wash  thoroughly  with  dilute  sulphur- 
etted-hydrogen water,  and  boil  the  filtrate,  adding  hydrochloric 
acid  and  chlorate  of  potash  to  oxidize  the  iron  and  sulphur. 
The  solution  is  now  ready  to  proceed  with  the  analysis  in  the 
usual  way.  If  no  members  of  the  sulphuretted-hydrogen  group 
are  present,  this  treatment  is  not  necessary. 

Treat  from  I  to  5  grammes  of  ore  (according  to  the  amount: 
of  Ni  and  Co  which  the  ore  contains)  with  pure  concentrated 
sulphuric,  nitric,  and  hydrochloric  acids  in  a  small  flask  similar 
to  the  flask  used  in  the  copper-assay.  For  i  gramme  of  ore 
use  about  5  cc.  of  sulphuric,  5  cc.  of  nitric,  and  3  cc.  of 

211 


212  A   MANUAL    OF  PRACTICAL  ASSAYING. 

hydrochloric  acid.  Heat  until  copious  fumes  of  sulphuric 
anhydride  are  given  off,  adding  more  sulphuric  acid,  if  neces- 
sary, to  avoid  reducing  the  mass  to  dryness.  Cool,  dilute  with 
cold  water,  filter,  and  wash  thoroughly  with  hot  water. 

Dilute  the  filtrate  or  the  oxidized  filtrate  from  the  precipi- 
tated sulphides,  if  sulphuretted  hydrogen  was  used,  with  water, 
and  gradually  add  ammonia-water,  with  constant  stirring,  until 
the  solution  is  decidedly  alkaline.  Filter  out  the  precipitated 
ferric  hydrate  and  wash  slightly  with  hot  water.  Dissolve  the 
precipitate  with  dilute  hydrochloric  acid,  dilute  with  water,  add 
pure  sodium  carbonate  until  a  slight  cloudiness  is  perceptible, and 
then  add  a  drop  of  dilute  hydrochloric  acid  to  clear  the  solu- 
tion. Now  add  from  7  to  15  grammes  of  pure  sodium  acetate, 
and  boil  to  precipitate  basic  acetates.  Filter  whilst  hot,  using 
the  filter-pump  if  the  precipitate  is  bulky.  Wash  with  hot 
water,  and  dissolve  the  precipitate  with  dilute  hydrochloric 
acid,  and  reprecipitate  as  basic  acetates,  as  before.  This  second 
basic-acetate  precipitation  is  unnecessary  if  the  amount  of 
iron  and  alumina  is  small ;  but  if  the  first  basic-acetate  precipi- 
tate is  large,  it  is  necessary  in  order  to  insure  all  the  nickel 
and  cobalt  passing  into  solution.  Combine  the  three  filtrates 
and  concentrate  to  400  or  500  cc.  by  evaporation,  acidify 
slightly  with  acetic  acid,  and  boil.  When  boiling  saturate  the 
solution  with  sulphuretted  hydrogen,  continuing  the  boiling 
whilst  passing  the  gas.  Filter  off  and  wash  the  precipitated 
sulphides  of  nickel  and  cobalt,  and  wash  thoroughly  with  sul- 
phuretted-hydrogen water.  To  recover  any  possible  traces  of 
nickel  or  cobalt  which  may  have  escaped,  acidify  the  filtrate 
with  a  little  acetic  acid  and  boil.  Should  any  precipitate  of 
sulphides  be  recovered  by  this  treatment  wash  it  and  the  main 
precipitate  from  the  filter  into  a  casserole,  dry  and  burn  the 
filters,  add  the  ashes  to  the  precipitates,  and  dissolve  with 
nitrohydrochloric  acid.  Evaporate  nearly  to  dryness  to  expel 
the  excess  of  acid,  dilute  with  water  and  add  a  solution  of  pure 
potassium  hydrate,  heat  for  some  time,  keeping  the  solution 
near  the  boiling-point,  and  then  filter  and  wash:  Wash  the 
precipitated  oxides  from  the  filter  into  a  beaker,  place  the 


NICKEL   AND    COBALT.  21$ 

beaker  under  the  funnel,  and  dissolve  what  remains  on  the 
filter  with  a  saturated  solution  of  pure  potassium  cyanide, 
allowing  the  solution  to  run  through  the  filter  into  the  beaker 
containing  the  oxides.  Warm  the  beaker  and  its  contents 
until  the  oxides  are  dissolved,  and  heat  to  boiling  to  expel  the 
free  hydrocyanic  acid.  Now  add  to  the  hot  solution  finely 
pulverized  and  elutriated  red  mercuric  oxide,  and  boil.  The 
whole  of  the  nickel  will  be  precipitated,  partly  as  cyanide  and 
partly  as  sesquioxide,  the  mercury  combining  with  the  free 
cyanogen.  Filter  off  this  precipitate,  wash,  dry,  and  ignite. 
The  ignited  precipitate  is  oxide  of  nickel  (NiO).  To  obtain 
the  weight  of  nickel,  multiply  the  weight  of  this  precipitate  by 
0.78667. 

The  filtrate  from  the  precipitated  nickel  contains  the  cobalt 
in  solution.  Carefully  neutralize  it  with  nitric  acid,  so  that  the 
solution  is  not  acid  and  not  strongly  alkaline.  Now  add  a 
solution  of  mercurous  nitrate  as  long  as  it  produces  a  precipi- 
tate of  mercury-cobaltocyanide.  Filter,  wash,  and  dry  the 
precipitate,  finally  igniting  in  a  strong  current  of  hydrogen  in 
a  Rose  crucible  so  as  to  reduce  the  precipitated  cobalt  to  the 
metallic  state.  Weigh  the  metallic  cobalt. 

Another  good  method  is  to  concentrate  the  combined 
filtrates  from  the  ammonia  and  basic-acetate  precipitations  to 
about  100  cc.,  render  the  solution  decidedly,  alkaline  by  the 
addition  of  a  little  ammonia,  transfer  to  a  weighed  platinum 
dish,  and  precipitate  the  nickel  and  cobalt  together  by  passing 
a  strong  galvanic  current,  keeping  the  solution  alkaline  with 
ammonia.  The  battery  used  for  the  generation  of  the  current 
is  the  same  as  that  used  in  the  precipitation  of  copper  electro- 
lytically,  two  or  three  Bunsen  cells  making  a  very  good  battery. 

The  nickel  and  cobalt  are  thrown  down  on  the  platinum  in 
the  form  of  a  metallic  coating.  When  they  are  completely 
precipitated  remove  the  dish,  wash  it  thoroughly  with  hot 
water,  dry,  and  weigh  it.  The  increase  in  weight  of  the  dish 
is  the  combined  weights  of  the  metallic  nickel  and  cobalt.  If 
it  is  necessary  to  determine  them  separately  dissolve,  the  pre- 


214  A   MANUAL   OF  PRACTICAL  ASSAYING. 

cipitate  in  nitric  acid  and  effect  the  separation  and  determina- 
tion as  above.     This  is  a  very  neat  and  accurate  method. 

The  ignited  oxide  of  nickel  is  liable  to  contain  impurities. 
To  determine  these,  transfer  the  ignited  oxide  to  a  beaker,  add 
water,  and  boil.  Filter,  and  wash  thoroughly  with  boiling 
water.  Dry,  and  ignite  the  oxide  of  nickel  again.  The  loss  in 
weight  is  probably  due  to  some  adhering  alkali.  Now  dissolve 
the  oxide  of  nickel  in  nitrohydrochloric  acid,  boil,  dilute,  filter, 
wash,  dry,  ignite,  and  weigh  any  undissolved  silica.  Deduct 
this  weight  from  the  weight  of  the  oxide  of  nickel.  Dilute 
the  filtrate  and  add  a  large  excess  of  ammonia,  and  filter  out 
any  precipitate  of  alumina  or  ferric  hydrate  which  may  form. 
Wash,  dry,  and  ignite  this  precipitate  and  deduct  its  weight 
from  the  weight  of  the  nickel  oxide.  From  the  true  weight  of 
the  nickel  oxide,  as  thus  determined,  calculate  the  weight  of 
the  metallic  nickel. 


CHAPTER  XXIII. 

CALCIUM  (Ca). 

LlME  (CaO)  is  usually  determined  gravimetrically  by  pre< 
cipitating  it  as  calcium  oxalate,  converting  the  precipitate 
into  a  sulphate,  and  weighing  as  calcium  sulphate ;  or  volu- 
metrically  by  precipitating  it  as  calcium  oxalate,  and  deter- 
mining, after  filtering  and  washing,  the  oxalic  acid  combined 
with  the  calcium  by  means  of  a  standard  solution  of  potassium 
permanganate.  The  second  method  is  much  more  rapid  than 
the  first,  and  is  fully  as  accurate,  if  proper  care  be  observed. 
(See  Fresenius,  Wiley  &  Sons'  edition  of  1881,  page  828.) 

The  solution  of  permanganate  used  may  be  the  same  as  is 
used  for  the  determination  of  iron,  and  may  be  standardized 
in  the  same  manner.  A  comparison  of  the  following  equation 
with  the  one  for  the  oxidation  of  ferrous  iron  to  ferric  iron 
by  permanganate  of  potassium  (see  Part  II,  Chapter  XVI) 
will  show  that  one  cc.  of  the  permanganate  solution  is  equal 
to  exactly  half  as  much  lime  (CaO)  as  iron,  the  molecular 
weight  of  lime  and  the  atomic  weight  of  iron  being  the  same: 

5CaC3O4  +  8H,S04  +  KaMn2O8  = 

5CaS04  +  2MnS04  +  KaSO4  +  2CO3  +  8H2O. 

Consequently,  if  I  cubic  centimetre  of  permanganate  solution 
equals  o.oio  gramme  of.  iron  it  will  equal  0.005  gramme  of 
lime. 

Limestones. — One  gramme  of  the  limestones  is  treated  as 
described  in  Chapter  I,  on  Silica.  The  iron  and  alumina  are 
precipitated  out  of  the  filtrate  from  the  silica,  as  described 

215 


2l6  A    MANUAL    OF  PRACTICAL  ASSAYING. 

in  Chapter  XVII,  on  Alumina.  The  filtrate  from  the  precipi- 
tated hydrates  of  iron  and  aluminium  is  then  ready  for  the 
precipitation  of  the  calcium,  provided  its  bulk  is  not  much 
over  100  cc.  If  much  iron  or  alumina  is  present  it  is  safer  to 
dissolve  the  precipitated  hydroxides  in  a  few  cc.  of  hydrochloric 
acid,  and  reprecipitate  with  ammonia,  combining  the  filtrate 
from  this  precipitate  with  the  first  filtrate  for  the  determination 
of  the  lime.  A  cubic  centimetre  of  ammonia  should  be  added, 
and  the  solution  brought  to  a  boil.  If  a  precipitate  other  than 
aluminium  or  ferric  hydrate  forms  (such  a  precipitate  should  be 
filtered  out,  and  added  to  the  previous  precipitate  of  hydrates), 
acidify  slightly  with  hydrochloric  acid,  and  make  alkaline  with 
ammonia.  This  is  done  to  introduce  sufficient  ammonium 
chloride  to  prevent  the  precipitation  of  magnesium  hydrate. 
The  lime  is  then  precipitated  as  an  oxalate  by  the  addition  of 
ammonium  oxalate  or  oxalic  acid.  If  oxalic  acid  is  used  there 
should  be  a  considerable  excess  of  ammonia  present  in  order 
that  the  solution  may  be  alkaline  after  the  addition  of  the 
oxalic  acid.  If  magnesia  is  present  the  ammonium  oxalate 
should  be  in  considerable  excess.  [According  to  Cairns,  40  cc. 
of  a  solution  of  ammonium  oxalate  prepared  by  dissolving  one 
part  of  oxalate  in  twenty-four  of  water.]  This  is  not  only  to 
precipitate  all  of  the  lime  as  oxalate,  but  to  convert  all  of 
the  magnesia  into  oxalate,  which  is  soluble.  Heat  nearly  to 
boiling  for  a  few  minutes,  and  then  filter.  If  the  solution  was 
brought  to  a  boil  before  precipitation,  and  a  good  filter-paper 
is  used,  there  will  be  no  danger  of  the  calcium  oxalate  running 
through  the  filter-paper.  Provided  magnesia  is  not  present, 
less  ammonium  oxalate  should  be  used,  and  the  filtration  may 
be  proceeded  with  as  follows  :  filter,  and  wash  the  precipitate 
out  of  the  beaker  on  to  the  filter-paper  with  boiling  water,  then 
wash  the  precipitate  on  the  filter-paper  with  boiling  water  until 
the  washings  no  longer  give  a  reaction  for  oxalic  acid.  Remove 
the  filter  and  contents  from  the  funnel,  and  spread  out  on 
a  watch-glass  somewhat  larger  than  the  paper.  Wash  into  a 
beaker  with  hot  water  from  a  wash-bottle  with  a  fine  jet>  and 
after  all  the  precipitate  is  removed  from  the  paper,  or  all  that 


CALCIUM.  217 

can  be  in  this  way,  wash  the  paper  with  some  dilute  sulphuric 
acid,  transferring  the  washings  to  the  beaker.  Sometimes  it  is 
difficult  to  remove  the  last  traces  of  calcium  oxalate  from  the 
paper  with  sulphuric  acid.  In  such  a  case  a  few  drops  of  dilute 
hydrochloric  acid  may  be  added  to  the  paper.  The  contents 
of  the  beaker  are  now  diluted  with  warm  water  to  about  100 
cc.,  15  cc.  sulphuric  acid  added,  and  the  solution  heated  to 
about  70°  C.  The  solution  is  now  ready  for  titration  with  a 
standard  solution  of  potassium  permanganate.  This  titration 
is  performed  in  the  same  manner  as  described  for  the  determi- 
nation of  the  standard  of  the  permanganate  solution  by  means 
of  oxalic  acid  (see  Chapter  XVI).  If  magnesia  is  present  it  is 
always  safest,  and  is  in  fact  absolutely  necessary  where  an 
accurate  determination  is  to  be  made,  to  dissolve  the  first 
precipitate  of  calcium  oxalate  in  hydrochloric  acid,  and  repre- 
cipitate,  on  account  of  the  magnesia  which  has  been  carried 
down  with  the  first  precipitate.  To  do  this  wash  the  precipitate 
into  a  beaker  as  before  (such  care  in  washing  the  precipitate  as 
before  is  not  necessary ;  in  fact,  it  need  only  be  filtered),  and 
dissolve  in  as  little  hot  dilute  hydrochloric  acid  as  possible. 
Dilute  to  about  50  cc.  with  boiling  water,  make  alkaline  with 
ammonia,  add  20  cc.  of  ammonium-oxalate  solution,  and  heat 
nearly  to  boiling.  Then  filter,  wash,  and  determine  the  lime 
as  above. 

The  second  filtrate  is  to  be  combined  with  the  first  for  the 
determination  of  magnesia.  (See  Chapter  XXIV.) 

If  desirable  the  lime  can  be  determined  gravimetrically,  as 
described  below,  although  the  experience  of  the  writer  is  that 
the  volumetric  determination  gives  fully  as  accurate  results,  and 
is  more  rapid. 

Clays,  Cements,  Feldspar,  etc.— Treat  the  substance  as 
described  in  Chapter  I,  and,  after  combining  the  filtrate  from 
the  insoluble,  and  the  silica  by  fusion,  proceed  as  above. 

Ores. — For  the  determination  of  lime  in  ores  the  method 
as  given  for  limestone  may  be  used.  In  the  cases  of  lead  ores 
it  is  necessary  to  first  remove  the  lead. 


218  A    MANUAL   OF  PRACTICAL   ASSAYING. 

Slag*. — For  the  determination  of  the  lime  in  a  slag  the  fol- 
lowing method  is  generally  used,  and  answers  all  requirements 
for  technical  purposes : 

The  filtrate  from  the  silica  (see  Chapter  I)  is  heated  to  boil- 
ing, made  alkaline  with  a  slight  excess  of  ammonia,  and  acidi- 
fied with  a  slight  excess  of  a  saturated  solution  of  oxalic  acid. 
Ammonia  is  then  added  until  the  solution  is  slightly  alkaline, 
and  then  a  solution  of  oxalic  acid  until  the  iron  precipitate  is 
dissolved.  The  solution  is  then  heated  to  boiling,  filtered  and 
washed,  the  lime  being  determined  volumetrically  as  above. 
The  precipitated  calcium  oxalate  should  be  white,  otherwise 
iron,  manganese,  etc.,  have  not  been  dissolved,  showing  an  in- 
sufficiency of  oxalic  acid.  Whilst  this  latter  method  is  not 
absolutely  accurate,  it  is  generally  sufficiently  accurate  for 
technical  purposes,  and  is  extremely  rapid ;  a  determination  of 
silica  and  lime  in  a  slag  having  frequently  been  made  by  the 
writer  in  from  an  hour  and  fifteen  minutes  to  an  hour  and  a 
half  whilst  doing  other  work. 

For  the  determination  of  the  lime  gravimetrically,  obtain 
the  precipitate  of  calcium  oxalate  as  described  above.  It  is 
necessary  to  wash  all  of  the  precipitate  out  of  the  beaker  and  on 
to  the  filter.  Some  of  the  precipitate  will  usually  adhere  to  the 
sides  of  the  beaker,  and  can  generally  be  removed  by  rubbing 
with  a  glass  rod  provided  with  a  rubber  on  the  end.  When  this 
treatment  fails  to  remove  all  of  the  precipitate  from  the  sides 
of  the  beaker,  dissolve  it  in  a  few  drops  of  hydrochloric  acid, 
add  a  few  cc.  of  boiling  water,  making  alkaline  with  ammonia, 
and  precipitate  with  ammonium  oxalate.  When  all  of  the  pre- 
cipitate is  transferred  to  the  filter,  wash  until  the  washings  no 
longer  give  a  reaction  for  oxalic  acid,  and  finally  wash  the  pre- 
cipitate down  into  the  point  of  the  filter.  Dry  the  filter-paper 
and  its  contents  in  a  hot-air  bath,  and  when  thoroughly  dry 
remove  from  the  funnel.  Transfer  the  precipitate  to  a  weighed 
platinum  crucible  by  inverting  the  filter-paper  over  the  crucible 
and  gently  rolling  between  the  fingers.  Roll  the  filter-paper 
and  the  small  amount  of  precipitate  adhering  to  it  into  a  ball, 
and  ignite  on  the  lid  of  the  crucible  over  the.  flame  of  a  burner 


CALCIUM,  219 

until  white.  Add  the  filter-ash  to  the  precipitate  in  the  cruci- 
ble, and  thoroughly  moisten  the  precipitate  with  strong  c.  p. 
sulphuric  acid,  place  the  lid  on  the  crucible,  and  expel  the 
excess  of  acid  by  heating  over  a  burner,  allowing  the  flame  to 
touch  only  the  edge  of  the  crucible  cover.  After  expelling  all 
free  sulphuric  acid,  ignite  strongly  over  a  blast-lamp  or  in  the 
muffle,  cool,  and  weigh. 

This  weight,  after  deducting  the  known  weights  of  the  cruci- 
ble and  filter-ash,  will  be  the  weight  of  the  calcium  sulphate. 
Multiply  this  weight  by  0.41176,  and  the  result  will  be  the 
weight  of  the  lime. 


CHAPTER   XXIV. 

MAGNESIUM   (Mg). 

MAGNESIA  (MgO)  is  universally  determined  by  precipitating 
it  as  ammonium-magnesium  phosphate,  converting  it  into  mag- 
nesium pyrophosphate  (Mg2P2O7)  by  ignition,  and  weighing  as 
such.  The  preparation  of  the  solution  for  the  precipitation  of 
the  magnesia  will  depend  upon  what  metals  are  present.  The 
metals  of  the  sulphuretted-hydrogen  group,  the  ammonium- 
sulphide  group,  and  barium,  strontium,  and  calcium,  should  be 
removed  before  the  precipitation  of  the  magnesia. 

The  solution  should  contain  ammonium  chloride  and  an 
excess  of  free  ammonia,  and  should  be  cold  before  adding  the 
hydrodisodium-phosphate  solution,  which  may  be  prepared  by 
dissolving  one  part  by  weight  of  the  salt  in  ten  parts  of  water. 
After  adding  the  phosphate  solution,  agitate  by  stirring  with  a 
glass  rod,  care  being  exercised  not  to  touch  the  sides  of  the 
beaker  with  the  rod,  as  that  will  cause  crystals  of  ammonium- 
magnesium  phosphate  to  adhere  to  the  sides  of  the  beaker,  and 
they  will  be  difficult  to  remove.  Cold,  and  frequent  agitation 
of  the  solution,  facilitate  the  precipitation,  and  it  is  a  good  plan 
to  set  the  beaker  in  a  dish  containing  ice-water  or  a  freezing 
mixture  and  stir  from  time  to  time.  Several  hours'  (from  2  to 
12)  standing  in  the  cold  are  necessary  to  complete  the  precipi- 
tation, the  time  depending  to  a  great  extent  on  the  amount  of 
magnesia  present.  After  allowing  to  stand  a  sufficient  length 
of  time,  remove  a  few  drops  of  the  clear  liquid  with  a  piece  of 
glass  tubing,  transfer  to  a  test-tube,  and  add  two  or  three  drops 
of  magnesia  mixture.  This  is  prepared  by  dissolving  one 
gramme  of  magnesium  sulphate  and  one  gramme  of  ammonium 
chloride  in  8  cc.  of  water  and  adding  3  cc.  of  ammonia.  If  a 

220 


MAGNESIUM.  221 

precipitate  forms  it  shows  that  sufficient  phosphate  solution 
was  added.  Should  no  precipitate  form  add  5  cc.  of  the  phos- 
phate solution,  stir,  and  proceed  as  before.  Provided  one 
gramme  of  substance  was  taken,  and  the  magnesia  is  not  over 
30  per  cent,  30  cc.  of  the  phosphate  solution  (prepared  as  above) 
and  added  at  first  will  serve  to  precipitate  all  of  the  magnesia. 
Filter  on  a  small  filter  and  wash  with  dilute  ammonia,  prepared 
by  adding  two  parts  of  water  to  one  part  of  ammonia,  until  the 
washings  no  longer  show  a  precipitate  upon  the  addition  of  a 
few  drops  of  silver-nitrate  solution,  after  having  previously 
acidified  them  with  c.  p.  nitric  acid.  Dry  the  filter  and  precipi- 
tate as  in  the  case  of  calcium  oxalate  (see  Chapter  XXIII),  and 
when  dry  transfer  the  precipitate  to  a  weighed  crucible,  and 
ignite  the  filter  on  the  lid  of  the  crucible  until  white.  Add  the 
filter-ash  to  the  contents  of  the  crucible,  and  ignite  strongly 
until  the  contents  of  the  crucible  are  white  or  nearly  so. 
Should  the  precipitate  be  of  a  dark  color,  moisten  with  a  few 
drops  of  nitric  acid,  and,  after  having  carefully  evaporated  off 
the  excess  of  acid,  ignite  again  strongly  until  the  precipitate 
assumes  a  light-gray  color.  Now  cool  and  weigh  the  crucible 
and  its  contents.  After  deducting  the  known  weight  of  the 
crucible  and  filter-ash,  the  remainder  will  be  the  weight  of  the 
magnesium  pyrophosphate.  Multiply  this  weight  by  0.36036, 
and  the  result  will  be  the  weight  of  the  magnesia  (MgO).  From 
this  calculate  the  percentage. 

Slags. — As  these  contain  all  the  impurities  of  the  ores  and 
fluxes  from  which  they  were  produced,  to  a  more  or  less  large 
extent,  a  separation  of  the  metals  of  the  different  groups  will 
be  necessary  before  precipitating  the  magnesia.  Dilute  the 
filtrate  from  the  silica  obtained  as  described  in  Chapter  I,  with 
distilled  water,  to  about  200  cc.,  and  pass  a  rapid  current  of 
sulphuretted-hydrogen  gas  through  the  solution,  filter  off  the 
precipitated  sulphides,  and  oxidize  the  filtrate  as  described  in 
Chapter  XVII.  Transfer  the  solution  to  a  flask  of  not  less 
than  500  cc.  capacity,  and  add  a  saturated  solution  of  sodium 
carbonate  until  a  slight  permanent  precipitate  forms.  Dissolve 
this  precipitate  in  a  slight  excess  of  acetic  acid,  add  about  10 


222  A   MANUAL   OF  PRACTICAL  ASSAYING. 

grammes  of  sodium  acetate,  dilute  to  about  300  cc.,  and  heat  to 
boiling.  Continue  to  boil  for  a  few  minutes,  and  filter  whilst 
hot,  washing  thoroughly  with  hot  water.*  Boil  the  filtrate 
from  the  precipitated  basic  acetates,  add  a  few  grammes  of 
sodium  acetate,  and  add  bromine-water  until  the  solution  has 
a  decided  yellow  color.  Continue  to  boil  and  add  bromine- 
water  for  some  time,  until  the  bromine  no  longer  produces  a 
precipitate  of  manganese  oxide.  Filter  out  the  precipitate  of 
manganese  oxide,  and,  to  be  sure  that  the  filtrate  contains  no 
manganese,  neutralize  it  with  sodium  carbonate,  acidify  with 
acetic  acid,  boil,  and  add  bromine.  If  a  precipitate  forms,  pro- 
ceed as  before.  When  the  solution  is  free  from  manganese 
acidify  it  thoroughly  with  acetic  acid,  boil,  and  while  boiling 
pass  a  rapid  current  of  sulphuretted-hydrogen  gas.  The  gas 
should  be  passed  for  from  10  to  30  minutes,  depending  upon 
the  amount  of  zinc  present.  By  this  means  the  zinc  is  pre- 
cipitated as  a  sulphide,  and  can  be  filtered  out.  Wash  with 
hot  water  by  decantation  once  or  twice,  and  then  wash 
thoroughly  with  sulphuretted-hydrogen  water.  It  is  best  to 
remove  the  beaker  containing  the  bulk  of  the  solution  from 
beneath  the  funnel,  and  filter  into  a  small  beaker,  changing  the 
beaker  frequently  on  account  of  the  liability  of  the  zinc  sulphide 
to  run  through  the  filter.  To  the  filtrate  from  the  zinc  sulphide 
add  I  cc.  of  hydrochloric  acid,  boil,  and  add  bromine-water  to 
oxidize  the  sulphur.  If  a  precipitate  of  sulphur  forms,  filter  it 
out.  The  solutions  now  contains  lime  and  magnesia.  The 
lime  is  precipitated  as  calcium  oxalate  in  the  manner  described 
in  Chapter  XXIII,  the  precaution  being  observed  to  dissolve 
the  precipitate  of  calcium  oxalate  in  a  little  hydrochloric  acid 
and  reprecipitate,  on  account  of  the  magnesia  which  may  be 
precipitated  together  with  the  lime.  The  filtrate  from  the 
calcium  oxalate  is  now  ready  for  the  precipitation  of  the  mag- 
nesia in  the  manner  described  above. 

*  When  considerable  quantities  of  iron,  alumina,  and  magnesia  are  present, 
it  is  best  to  dissolve  the  precipitate  in  a  little  hot  dilute  hydrochloric  acid,  and 
reprecipitate  as  basic  acetates  in  the  manner  described,  adding  the  second  fil- 
trate to  the  first. 


MA  GNESIUM.  22$ 

Silver,  Copper,  and  Lead  Ores. — Proceed  as  above,  except 
that  when  manganese  and  zinc  are  not  present  the  lime  can  be 
precipitated  in  the  filtrate  from  the  precipitate  of  the  basic 
acetates  of  iron  and  alumina,  the  treatment  with  bromine,  and 
subsequently  with  sulphuretted  hydrogen,  being  omitted. 

Limestones,  Clays,  Cements,  etc. — As  these  substances 
seldom  contain  any  of  the  metals  of  the  sulphuretted-hydrogen 
group,  proceed  as  in  the  determination  of  lime  in  limestones 
(see  Chapter  XXIII),  and  precipitate  the  magnesia  in  the 
filtrate  from  the  calcium  oxalate  as  above. 

The  above  examples  will  serve  for  nearly  every  case  likely 
to  arise. 


CHAPTER   XXV. 
BARIUM  (Ba). 

BARIUM  is  universally  precipitated  as  a  sulphate  and 
weighed  as  such  (BaSO4). 

The  following  method  will  serve  for  all  ores  and  furnace- 
products  : 

Dissolve  as  described  in  Chapter  I,  taking  the  precaution 
to  add  a  few  drops  of  sulphuric  acid  in  addition  to  the  hydro- 
chloric and  nitric  acids,  to  precipitate  the  barium  as  sulphate 
with  the  silica.  Evaporate  to  dryness,  dissolve  in  hydrochloric 
acid,  boil,  add  water,  filter  and  wash  thoroughly,  and  ignite.  If 
the  silica  is  to  be  determined,  weigh  the  insoluble  residue  and 
determine  the  barium  as  follows :  Fuse  the  insoluble  residue 
with  from  one  to  five  grammes  (depending  on  its  amount)  of 
carbonate  of  soda  (see  Chapter  I).  Dissolve  the  fusion  in  hot 
water  and  boil.  Filter  through  a  small  filter,  and  wash  until 
the  washings  no  longer  show  a  reaction  for  sulphuric  acid,  which 
can  be  determined  by  acidifying  some  of  the  washings  in  a  test- 
tube  with  hydrochloric  acid  and  adding  a  few  drops  of  barium- 
chloride  solution.  Should  no  precipitate  form,  the  barium  car- 
bonate remaining  behind  on  the  filter  is  washed  sufficiently. 
Dissolve  the  precipitate  on  the  filter  in  dilute  hydrochloric 
acid,  allowing  the  solution  to  run  into  a  small  beaker.  The 
funnel  should  be  covered  with  a  watch-glass  to  prevent  loss  by 
effervescence  when  the  acid  is  added.  Wash  off  the  watch-glass 
and  sides  of  the  funnel  with  hot  water,  and  finally  drop  a  few 
drops  of  hydrochloric  acid  around  the  edges  of  the  filter-paper 

224 


BARIUM.  225 

and  wash  thoroughly  with  hot  water.  The  filtrate  should  be 
perfectly  clear,  and  should  be  brought  to  a  boil  when  it  is  ready 
for  the  precipitation  of  the  barium,  which  can  be  accomplished 
by  adding  sulphuric  acid  to  the  solution.  From  a  few  drops 
to  two  cc.  of  dilute  sulphuric  acid  should  be  added,  depending 
on  the  amount  of  barium  present.  The  solution  should  be 
allowed  to  stand  for  some  time  until  the  precipitate  partially 
settles  before  filtering.  If  a  good  filter-paper,  such  as  Schlei- 
cher  &  Schuell's,  is  used,  it  is  not  necessary  to  allow  the  solu- 
tion to  stand  until  the  precipitate  settles  absolutely,  as  with 
such  a  filter  it  will  seldom  run  through.  A  good  plan  is  to 
filter  off  into  a  small  beaker,  changing  the  beaker  frequently,  so 
if  any  of  the  precipitate  should  run  through  the  filter  it  will 
not  be  necessary  to  refilter  such  a  large  amount  of  solution. 
The  first  filtrate  should  be  tested  with  a  few  drops  of  sulphuric 
acid  to  determine  whether  all  of  the  barium  has  been  precipi- 
tated. After  the  solution  is  all  filtered  wash  what  remains  in 
the  beaker  on  to  the  filter  with  hot  water,  and  wash  the  pre"- 
cipitate  on  the  filter  once  or  twice  with  hot  water,  finally  wash- 
ing the  precipitate  down  into  the  point  of  the  filter.  Dry,  and 
ignite  in  the  manner  described  for  the  precipitate  of  magnesia 
pyrophosphate  (Chapter  XXIV).  A  small  filter-paper  should 
be  used,  as  the  carbon  of  the  filter-paper  is  liable  to  reduce 
barium  sulphate  to  a  sulphide.  When  much  of  the  precipitate 
adheres  to  the  filter-paper  moisten  its  ash,  after  ignition,  with 
a  few  drops  of  nitric  acid,  and  ignite  again.  The  precipitate 
should  be  perfectly  white,  and  can  be  transferred  from  the 
crucible  to  the  watch-glass  of  the  balance  and  weighed  directly. 
This  weight,  less  the  known  weight  of  the  filter-ash,  will  be  the 
weight  of  the  barium  sulphate.  To  obtain  the  weight  of  the 
baryta  (BaO)  multiply  this  weight  by  0.65636. 

For  the  rapid  determination  of  baryta  and  silica  in  lead 
slags  the  following  method  answers  for  technical  purposes: 
Treat  0.5  gm.  with  water  and  hydrochloric  acid  in  a  casserole, 
heat,  add  water,  filter,  and  determine  the  silica  as  usual.  This 
insoluble  residue  may  be  considered  as  silica.  Treat  another 


226  A   MANUAL   OF  PRACTICAL  ASSAYING. 

portion  (0.5  gm.)  with  water,  hydrochloric  acid,  and  a  few 
drops  of  sulphuric  acid.  Evaporate  to  dryness,  heat,  dissolve 
in  water  and  hydrochloric  acid,  and  determine  the  insoluble 
residue  as  usual.  This  insoluble  residue  may  be  considered  as 
consisting  of  silica  and  barium  sulphate. 


CHAPTER  XXVI. 
POTASSIUM  (K)  AND  SODIUM  (Na). 

ONE  of  the  two  following  methods  will  be  used,  according  to 
whether  the  substance  is  decomposed  by  acids  or  not : 

First  Method. —  The  Substance  is  decomposed  by  Acids. — 
Dissolve  from  0.5  to  5.0  grammes  in  hydrochloric  acid,  add 
bromine  or  chlorine  water,  and  heat  to  boiling.  Evaporate  to 
dryness  if  necessary,  and  proceed  as  in  the  determination  of 
silica  (Chapter  I).  To  the  filtrate  from  the  silica  add  ammonia  in 
slight  excess  (if  any  members  of  the  sulphuretted-hydrogen 
group  are  present  they  must  be  removed,  as  in  the  case  of  de- 
termination of  alumina,  Chap.  XVII),  and  ammonium  carbonate, 
and  allow  to  stand  for  a  few  hours.  Filter,  wash,  evaporate 
the  filtrate  and  washings  to  dryness  in  a  platinum  dish,  and  ex- 
pel the  ammonia  salts  by  igniting  to  a  point  just  below  redness. 
Dissolve  in  water,  add  solution  of  barium  hydrate  until  the 
fluid  is  decidedly  alkaline,  filter  and  wash  well,  and  add  to  the 
filtrate  solution  of  ammonium  carbonate  as  long  as  it  produces 
a  precipitate  ;  allow  the  solution  to  stand  for  a  short  time,  filter 
out  the  barium  carbonate,  and  wash  it  until  the  washings  do 
not  render  silver  nitrate  turbid.  Now  add  a  few  drops  of 
hydrochloric  acid  to  the  filtrate,  and  evaporate  it  to.  dryness 
in  a  weighed  platinum  dish,  ignite  to  a  slight-red  heat,  cool 
and  weigh  the  mixed  chlorides  of  sodium  and  potassium. 
Where  an  accurate  determination  is  required,  it  is  best  to  dis- 
solve the  mixed  chlorides  in  water  and  repeat  the  treatment 
with  barium  hydrate  and  ammonium  carbonate,  and  again  evap- 
orate and  weigh. 

The  weight  of  sodium  and  potassium  present  may  now  be 

227 


228  A   MANUAL   OF  PRACTICAL  ASSAYING. 

determined  indirectly  as  follows  :  Dissolve  the  combined  chlo- 
rides in  warm  water,  add  a  few  drops  of  a  saturated  solution  of 
potassium  chromate,  and  add  from  a  burette  a  standardized 
solution  of  silver  nitrate  until  the  red  color  of  silver  chromate 
appears.  From  the  number  of  cc.  of  standard  silver  nitrate-solu- 
tion used  calculate  the  weight  of  chlorine  present,  as  described 
below.  The  weight  of  chlorine  present  having  been  thus  de- 
termined, the  weights  of  the  sodium  and  potassium  present  may 
be  calculated  as  follows:  Suppose  we  have  found  i.o  gramme 
of  sodium  and  potassium  chlorides  and  0.563  gramme  of  chlo- 
rine present  in  the  combined  chlorides. 

35.4  (at.  wt.  Cl)  :  74.4  (mol.  wt.  KC1)  :  :  0.563   (Cl  found)  :  x. 

x  =  1.18326. 

If  all  of  the  Cl  present  were  combined  with  K,  the  weight 
of  the  chloride  would  amount  to  1.18326.  As  the  combined 
chlorides  weigh  less,  NaCl  is  present,  and  in  a  quantity  pro- 
portional to  the  difference  (dif.  —  1.18326  —  i.o  —  0.18326). 
The  difference  between  the  molecular  weight  of  KCl  and  that 
of  NaCl  (16.0)  is  to  the  molecular  weight  of  NaCl  (58.4)  as  the 
difference  found  is  to  the  NaCl  present ;  or, 

16  :  5.84  : :  0.18326  :  x  (NaCl  present). 
x  (NaCl  present)  =  0.67015  gms. 

KCl  present  =  i.o  —  0.67015  =  0.32985. 

The  above  illustrates  the  method  of  calculating  results. 

To  prepare  the  standard  silver-nitrate  solution,  dissolve  from 
17  to  1 8  grammes  of  pure  nitrate  of  silver  in  one  litre  of  dis- 
tilled water.  To  standardize  the  solution,  dissolve  I  gramme 
of  pure  fused  sodium  chloride  in  one  litre  of  water,  pour  exact- 
ly loo  cc.  of  the  solution  into  a  beaker,  add  three  drops  of  a 
saturate  solution  of  potassium  chromate,  and  drop  in  from  the 
burette  the  silver  solution  until  the  red  color  of  silver  chromate 
appears.  The  known  quantity  of  chlorine,  in  the  100  cc.  of  salt 
solution,  divided  by  the  number  of  cc.  of  silver  solution  used, 
will  give  the  value  of  I  cc.  of  the  latter. 


POTASSIUM  AND   SODIUM.  2  29 

In  the  case  of  analyses  where  extreme  accuracy  is  required 
the  potassium  may  be  determined  directly  as  follows,  and  the 
sodium  by  difference  :  Dissolve  the  combined  chlorides  (after 
having  weighed  them)  in  warm  water,  and  if  the  solution  is  com- 
plete, transfer  it  to  a  small  casserole,  add  3  to  4  drops  of  hydro- 
chloric acid  and  a  solution  of  potassium  tetrachloride  (as  much 
as  contains  an  amount  of  the  salt  equal  to  about  four  times  the 
weight  of  the  combined  chlorides)  and  evaporate  on  the  water- 
bath  until  the  mass  is  pasty.  Now  add  to  the  casserole  about 
5$  cc.  of  85  per  cent  alcohol,  and  heat  for  a  few  minutes  on  the 
water-bath.  Then  wash  into  a  small  flask  (which  we  will  desig- 
nate as  A)  the  contents  of  the  casserole  with  alcohol  (85  per 
cent),  and  cork  the  flask  immediately.  After  the  precipitate  of 
potassium  platinochloride  has  entirely  settled,  and  the  fluid 
shows  by  its  yellow  color  that  sufficient  platinum  tetrachloride 
has  been  added,  pour  off  the  clear  fluid  into  a  small  flask 
marked  B,  as  completely  as  possible  without  transferring  any 
of  the  precipitate,  cork  it,  and  allow  it  to  stand  long  enough  for 
any  particles  of  potassium  platinochloride,  which  may  have 
passed  over  with  the  fluid  from  flask  A,  to  subside.  Then  pour 
into  flask  A  20  or  30  cc.  of  85  per  cent  alcohol,  cork  it,  and 
after  agitating  it  gently  set  it  aside  until  the  contents  of  flask 
B  are  disposed  of.  Pour  the  contents  of  B  into  a  dish,  add 
about  10  cc.  of  water,  and  proceed  to  evaporate  off  the  alcohol 
on  a  water-bath.  Should  there  be  any  particles  of  the  precipi- 
tate in  the  fluid,  first  pour  off  as  much  as  possible  into  the  dish, 
without  disturbing  the  precipitate  and  evaporate  it  as  above,  and 
pour  the  rest,  with  the  precipitate,  on  a  filter.  Add  this  fil- 
trate to  the  fluid  already  evaporating.  Keep  the  funnel  covered 
with  a  glass  while  filtering.  After  all  the  fluid  has  thus  been 
transferred  to  the  dish  for  evaporation,  pour  upon  the  same 
filter  the  contents  of  flask  A,  washing  the  precipitate  onto  the 
filter  with  85  per  cent  alcohol.  Dry  the  filter  and  contents  in 
an  air-bath  at  100°  C.  Ignite  the  dry  precipitate,  rolled  up  in 
the  filter,  in  a  weighed  crucible,  applying  the  heat  very  gently 
at  first,  and  keeping  the  crucible  covered  until  the  filter-paper 
is  charred.  Then  remove  the  cover  and  ignite  at  a  higher  heat 


230  A   MANUAL   OF  PRACTICAL  ASSAYING. 

until  the  filter  is  entirely  consumed.  Allow  the  crucible  to  cool, 
add  a  little  oxalic  acid,  heat  gently  at  first,  until  the  water  of 
crystallization  of  the  oxalic  acid  is  expelled,  and  then  more 
intensely  until  the  acid  is  decomposed  and  all  the  carbon  con- 
sumed. Cool  the  crucible,  and  wash  by  decantation  with  hot 
water  as  long  as  the  wash-water  becomes  turbid  from  the  forma- 
tion of  silver  chloride  when  treated  with  silver  nitrate.  By  this 
means  the  double  chloride  is  decomposed,  and  all  the  potas- 
sium and  chlorine  washed  out,  leaving  only  spongy  platinum. 
Heat  alone  fails  to  decompose  the  compound  completely. 
After  the  platinum  is  sufficiently  washed,  dry  th'e  crucible  and 
contents,  and  ignite  until  everything  is  consumed  but  spongy 
platinum.  Cool  and  weigh.  This  weight,  less  the  known 
weight. of  the  crucible  and  filter-ash,  will  be  the  weight  of  the 
platinum  combined  with  the  potassium  as  potassium-platinic 
chloride  (PtCl4,2KCl).  To  obtain  the  weight  of  the  potas- 
sium multiply  the  weight  of  the  platinum  found  by  0.39594. 

After  all  the  alcohol  has  been  expelled  from  the  original 
filtrate  by  evaporation,  as  directed  above,  add  I  cc.  of  platinum- 
tetrachloride  solution  and  a  small  quantity  of  pure  sodium 
chloride ;  continue  the  evaporation  to  pasty  consistency,  treat 
with  alcohol,  and  proceed  as  directed  for  the  treatment  of  the 
main  precipitate.  The  sodium  chloride  has  a  tendency  to 
prevent  the  decomposition  of  the  platinum  chloride  while 
evaporating. 

Should  the  solution  of  the  combined  chlorides  be  incom- 
plete, filter,  and  evaporate  the  filtrate  to  dryness,  as  directed ; 
weigh,  and  dissolve  in  warm  water.  Now  determine  the  potas- 
sium, as  directed  above. 

Second  Method. — The  Substance  is  not  entirely  decomposed 
by  Acids. — The  substance  can  be  fused  with  sodium  carbonate 
and  the  silica  separated  as  usual  (Chap.  I),  and  the  determina- 
tion proceeded  with  as  above;  or  the  method  of  Prof.  J.  L. 
Smith*  can  be  adopted.  This  method  is  as  follows:  Treat 

*  Am.  Jour.  Sci.  and  Arts,  Vol.  I,  p.  269  (1871);  Crooks,  Select  Methods, 
p.  409- 


POTASSIUM  AND   SODIUM.  231 

0.5  to  i.o  gm.  of  finely  pulverized  silicate  in  an  agate  or 
glazed  porcelain  mortar  with  an  equal  amount  of  granular 
ammonium  chloride,  rubbing  the  two  together  intimately. 
Add  eight  parts  of  pure  calcium  carbonate  in  three  or  four 
portions,  mixing  thoroughly  after  each  addition.  Transfer 
the  contents  of  the  mortar  completely  to  the  crucible,  and  tap 
gently  until  its  contents  are  settled.  It  is  then  clasped  by  a 
metallic  clamp  in  an  inclined  position,  and  the  heat  of  a  small 
Bunsen  burner  is  now  brought  to  bear  upon  the  crucible  just 
above  the  top  of  the  mixture,  and  gradually  carried  toward  the 
lower  part,  until  the  ammonium  chloride  is  completely  decom- 
posed, which  takes  about  five  minutes.  The  heat  is  now  raised 
gradually  to  a  bright  red,  and  kept  there  for  about  forty  min- 
utes. It  is  best  not  to  have  too  intense  a  heat,  as  that  would 
vitrify  the  mass  too  much.  The  crucible  is  now  cooled,  and 
when  cool  its  contents  will  be  found  to  be  more  or  less 
agglomerated,  in  the  form  of  a  semi-fused  mass.  The  mass  is 
now  transferred  to  a  small  casserole,  and  what  adheres  to  the 
crucible  is  removed  with  warm  distilled  water,  and  sufficient 
water  added  to  bring  the  bulk  of  the  solution  up  to  about 
75  cc.  The  contents  of  the  casserole  are  now  brought  to  the 
boiling-point,  when  the  mass  will  begin  to  slack.  After  the 
mass  is  completely  slacked  and  disintegrated,  the  analysis  is 
proceeded  with  as  follows :  Filter  off  the  contents  of  the  casse- 
role on  a  good-sized  filter,  and  wash  well  with  distilled  water. 
The  filtrate  will  contain  in  solution  all  the  alkalies,  with  some 
chloride  and  hydrate  of  lime.  Proceed  to  determine  the 
potassium  and  sodium  in  this  filtrate  in  the  manner  described 
in  the  First  Method,  by  the  addition  of  ammonium  carbonate, 
etc. 


PAKT  III. 


CHAPTER   I. 
ASSAY   OF   BASE   BULLION. 

FOUR  samples  (see  Fig.  7)  are  cut  from  the  small  sample 
bar  with  a  cold-chisel.  From  each  of  these  samples  J  assay- 
ton  is  accurately  weighed  out  for  cupellation,  it  being  a  good 
plan  to  pound  each  sample  into  a  cube  before  finishing  the 
weighing. 

Cupellation. — Each  -J-  A.  T.  sample  is  now  cupelled  sepa- 
rately. In  the  case  of  impure  bullion  each  sample  should  be 
scorified  with  a  little  borax  before  cupellation.  In  case  the 
lead  is  very  impure  and  contains  a  good  deal  of  copper,  a  little 
test-lead  will  help  the  scorification.  Some  assayers  prefer  to 
scorify  all  samples  before  cupellation,  contending  that  the  loss 
of  silver  in  scorification  is  less  than  the  loss  in  cupellation. 

The  cupels  should  weigh  about  20  gms.  each,  and  should 
be  heated  in  the  muffle  before  introducing  the  sample  for 
cupellation.  After  dropping  the  samples  into  the  cupel  the 
door  of  the  muffle  should  be  closed  until  the  samples  are 
melted  and  cupellation  begins.  As  soon  as  the  samples  begin 
to  cupel  the  door  is  opened,  and  the  cupellation  is  contin- 
ued at  the  proper  temperature  until  the  buttons  "  brighten." 
The  temperature  of  cupellation  should  be  properly  regulated. 
The  cupels  should  always  show  "feather  litharge"  around  the 
edges,  which  they  will  not  do  if  the  temperature  is  too  high. 
On  the  other  hand,  the  temperature  should  not  be  too  low,  as 

232 


ASSAY  OF  BASE  BULLION.  233 

in  this  case  the  loss  of  silver  will  be  high,  and  the  buttons  are 
apt  to  "freeze"  and  ruin  the  assay.  The  proper  temperature 
is  something  which  can  only  be  learned  by  experience.  When 
the  bullion  is  rich  and  the  buttons,  consequently,  large,  it  is 
a  good  plan  to  have  some  cupels  in  the  rear  of  the  muffle, 
to  cover  the  cupels  containing  the  buttons  just  after  they 
"  brighten."  The  cupels  should  be  placed  in  a  hot  part  of  the 
muffle  just  before  "  brightening,"  and  should  be  gradually 
removed  after  "  brightening,"  in  order  to  prevent  "  spitting." 
A  button  which  has  "  spit "  or  "  sprouted  "  should  always  be 
rejected.  When  the  cupels  are  cool  the  buttons  are  ready  for 
weighing. 

Weighing. — The  buttons  are  best  removed  from  the  cupel 
by  means  of  a  pair  of  pliers,  and  should  be  brushed  off  with  a 
wire-brush  to  remove  any  particles  of  litharge  or  bone-ash 
which  may  adhere  to  the  bottom.  The  buttons  are  now  ready 
for  weighing  on  the  button-balance,  and  should  agree  together 
closely.  The  agreement  should  be  within  about  0.5  ounces  on 
a  bullion  of  from  200  to  400  ounces.  After  weighing,  the  but- ' 
tons  should  be  flattened  out  with  a  few  light  blows,  when  they 
are  ready  for  parting. 

Parting. — The  parting  can  be  performed  in  a  small  porce- 
lain crucible  or,  preferably,  a  glass  matrass  or  test-tube.  Two 
of  the  flattened  buttons  are  introduced  into  each  matrass,  and 
c.  p.  nitric  acid  of  20°  Baume  added.  The  matrass  is  now  grad- 
ually warmed  on  an  iron  plate  or  sand-bath  until  the  silver  is 
all  dissolved.  The  contents  of  the  matrass  are  now  boiled  for  a 
few  minutes  and  then  removed  from  the  heat.  After  shaking 
gently  to  bring  all  the  fine  particles  of  gold  into  one  mass, 
the  solution  is  poured  off.  Fresh  acid  of  32°  Baume  is  now- 
added,  and  the  gold  boiled  for  three  minutes.  It  is  again 
brought  into  one  mass,  if  necessary,  and  the  acid  decanted  off. 
The  gold  is  now  washed  three  times  by  decantation  with  dis- 
tilled water  (free  from  chlorides),  the  matrass  filled  with  dis- 
tilled water  and  inverted  in  a  small  porcelain  crucible.  After 
the  gold  has  settled  to  the  bottom  the  matrass  is  removed  and 
the  water  poured  off,  the  last  drops  of  water  being  readily  re- 


234  A   MANUAL   OF  PRACTICAL  ASSAYING. 

moved  by  suction,  through  a  small  piece  of  glass  tubing  drawn 
to  a  point  at  the  end.  The  crucible  is  dried,  and  finally  ignited 
at  a  red  heat,  when  the  gold  is  ready  for  weighing  on  the  gold 
balance.  The  duplicates  should  agree  almost  exactly. 

Special  Method. — In  the  case  of  extremely  impure  bullion, 
this  method  may  have  to  be  adopted.  Prepare  the  sample  as 
described  in  Part  I,  Chapter  II,  weighing  the  dross  and  the  bar 
separately.  Weigh  out  four  samples,  of  £  A.  T.  each,  of  the 
dross,  scorify,  cupel,  and  part,  as  described  above.  Determine 
the  gold  and  silver  in  the  bar  as  described  above. 

The  manner  of  calculating  the  results  is  best  illustrated  by 
an  example  : 

Bar  weighs . . , 4.25  Ibs. 

Dross  weighs 1.50    " 


Total  weight  of  sample  (after  melting).     5.75  Ibs. 
Bar-assays  : 

Ag  ...............................  405.00  oz. 

Au  ...............................       i  .00    " 

Dross-assays  : 

Ag  ..............................   806.00  oz. 

Au  ............  ...................       3.50    " 


Then  -      X  405  —  0.860625, 


_        X  806  =  0.6045, 

2OOO 

the  total  ounces  of  silver  in  the  bar  and  dross. 
Hence  the  total  ounces  of  silver  in  the  sample 

=  0.86025  +0.6045  =  1.465125. 


Now  1.465125  X  =  509.61, 

the  ounces  of  silver,  per  ton  of  2000  pounds,  in  the  sample. 


ASSAY  OF  BASE  BULLION.  23$ 

In  the  same  manner  we  have  for  the  gold 

4^>  x  i.o  =  0.002125,     and     -ii  X  3.5  =  0.002625. 

2000  2OOO 

Hence 

2OOO 

0.002125-1-0.002625  =0.00475,    and    0.00475  X =  1.65, 

the  assay-value  of  the  sample  in  ounces  gold  per  ton. 
Hence  the  assay-value  of  the  bullion  is: 

Ag 509.61 

Au 1.65 

The  results  may  also  be  calculated  according  to  the  formulae 
given  in  Part  III,  Chapter  VIII,  in  which  case  the  bullion  and 
dross  are  weighed  in  grammes. 


CHAPTER  II. 

ASSAY  OF  SILVER  BULLION. 

FOR  the  determination  of  silver  in  silver  bullion  any  of  the 
following  methods  are  applicable,  but  the  first  two  are  the 
only  ones  generally  used  in  the  United  States. 

The  first  method  is  universal  in  its  application,  and  is  the 
method  generally  adopted  by  our  Western  metallurgical  estab- 
lishments, although  some  refiners  use  the  second  method,  whilst 
some  works  use  both  the  first  and  second  methods,  using  one 
as  a  check  on  the  other. 

The  first  method  is  preferable  when  the  bullion  contains 
mercury,  as  in  the  case  of  retorted  bullion  from  a  pan-amalga- 
mation mill. 

The  second  method* is  the  one  which  has  been  adopted  by 
the  U.  S.  Government  for  the  determination  of  the  fineness  of 
silver  bullion  in  the  U.  S.  mints  and  assay-offices. 

The  fineness  or  silver  and  gold  contents  of  the  bullion  is 
always  reported  in  thousandths  ;  i.e.,  so  many  degrees  or  parts 
of  silver  or  gold  in  one  thousand  parts  of  bullion.  For  example, 
we  say  a  bullion  is  990  silver  and  5  gold  fine ;  that  is,  it  con- 
tains 99  per  cent  of  silver  and  0.5  per  cent  of  gold. 

The  sample  of  bullion  should  always  be  annealed,  and  ham- 
mered or  rolled  out  thin  so  that  it  can  be  cut  readily  with  a 
pair  of  scissors.  A  small  set  of  rolls,  to  be  kept  only  for  this 
purpose,  will  be  found  very  convenient  when  many  assays  are 
to  be  made. 

First  Method  :  By  cupellation  with  pure  lead.  Fire-assay. 

236 


ASSAY  OF  SILVER  BULLION.  237 

Second  Method  :  Volumetrically  by  means  of  a  standard 
solution  of  sodium  chloride.  Gay-Lussac's  method. 

Third  Method:  Volumetrically  by  means  of  a  standard  so-1 
lution  of  potassium  sulphocyanide.  Volhard's  method. 

The  first  and  second  methods  require  a  preliminary  assay 
to  determine  the  approximate  fineness  of  the  bullion,  unless 
this  is  known.  The  third  method  requires  no  preliminary 
assay. 

Preliminary  Assay. — To  determine  the  approximate  fine- 
ness of  the  bullion  weigh  out  0.500  gramme  of  bullion  (the 
bullion  and  buttons  should  be  weighed  on  the  button-balance), 
wrap  in  from  5.0  to  10.0  grammes  of  pure  lead-foil,  and  cupel 
in  the  muffle-furnace,  using  a  small  cupel  weighing  about  10  to 
12  grammes.  The  cupel  should  be  hot  before  placing  the 
button  in  it,  and  the  door  of  the  muffle  should  be  closed  until 
cupellation  commences.  As  soon  as  cupellation  begins  the 
door  is  opened  and  the  cupel  moved  to  the  front  of  the  muffle. 
The  temperature  is  the  most  important  point  in  this  operation. 
The  assay  should  run  sufficiently  cold  to  allow  feather  litharge 
to  form  on  the  cupel,  but  not  so  cold  that  there  will  be  danger 
of  the  button  freezing.  The  proper  temperature  is  something 
.  which  can  only  be  gauged  by  experience  ;  after  considerable 
practice  with  this  method  the  assayer  will  be  able  to  control  the 
temperature  within  comparatively  narrow  limits.  Toward  the 
latter  part  of  the  cupellation  and  just  before  the  button 
brightens  the  cupel  should  be  moved  back  in  the  muffle.  After 
the  play  of  colors  on  the  button  has  ceased,  the  button  should 
be  covered  with  a  hot  cupel ;  but  before  covering,  it  should  be 
allowed  to  remain  for  about  a  minute  to  remove  the  last  traces 
of  lead.  The  assay  should  be  gradually  removed  from  the 
furnace  to  prevent  spitting  or  sprouting.  Should  the  button 
sprout,  the  assay  should  be  discarded.  When  the  cupel  is 
cold  the  fietttorrr  is  removed  by  a  pair  of  pliers,  and  brushed 


with  a  stiff  brush  to  remove  adhering  particles  of  bone-ash,  etc. 
The  weight  of  this  button  gives  the  amount  of  pure  silver  to 
be  taken  for  the  proof-  or  check-assay  if  the  first  method  is 
adopted  or  the  weight  of  bullion  to  be  taken  for  assay  if 


238 


A   MANUAL    OF  PRACTICAL  ASSAYING. 


the  second   method  is  adopted,  according   to   the  following 
table : 


Preliminary  Assay  of 
500  mgs.  gave  Ag,  mgs. 

Silver  to  be  used  in  Proof, 
mgs. 

Bullion  to  be  used  for 
Volumetric  Assay,  gms. 

Weight  of  sheet 
lead  to  be  used, 
gms. 

475 

480 

1.042 

5 

450 

455  to  4160 

.091 

7 

425 

430  to  435 

.156 

8 

400 

405  to  410 

.227 

10 

375 

380  to  385 

.307 

ii 

350 

355  to  360 

•399 

12 

325 

330  to  335 

•504 

13 

300 

305  to  310 

.610 

15 

250 

255  to  260 

.922 

17 

200 

2O5  10  2IO 

2.380 

T9 

150 

155  to  160 

3-125 

20 

First  Method. — The  check-  or  proof-assay  should  not  only 
contain  very  approximately  the  same  amount  of  silver  which 
the  bullion  contains,  but  approximately  the  same  amount  of 
copper  and  lead  as  the  bullion.  Should  the  bullion  contain 
much  gold,  the  proof  should  contain  gold  in  the  same  propor- 
tion. Should  the  bullion  contain  much  copper,  the  amount  can 
be  quickly  ascertained  by  dissolving  0.5  gramme  of  bullion  in 
dilute  nitric  acid,  adding  a  very  slight  excess  of  hydrochloric 
acid  to  precipitate  the  silver,  filtering  off  the  precipitated  silver 
chloride,  and  washing  the  precipitate  with  hot  water.  The 
filtrate  is  now  rendered  alkaline  with  ammonia,  and  the  copper 
determined  by  titration  with  a  standard  solution  of  potassium 
cyanide.  (See  Part  II,  Chapter  XIII.)  Or  the  copper  may  be 
determined  quickly  by  the  colorimetric  test.  (See  Part  II, 
Chapter  XIII.)  In  the  case  of  quite  fine  bullion,  as  the  bullion 
from  the  cupellation  process,  the  copper  can  be  disregarded. 
The  method  of  making  up  the  proof  is  best  illustrated  by  an 
example,  as  follows  :  Suppose  the  preliminary  assay  gave  375 
mgs.  of  silver  and  showed  the  bullion  to  contain  20  per  cent 
copper.  The  table  shows  that  we  would  have  to  weigh  out 
from  380  to  385  mgs.  o!  pure  silver,  and  that  11  gms.  of  lead 
would  be  required  for  cupellation.  To  this  should  be  added 


ASSAY  OF  SILVER  BULLION.  239 

100  mgs.  of  pure  copper-foil  and  25  mgs.  of  lead.  The  whole 
is  wrapped  in  the  1 1  gms.  of  sheet  lead  when  it  is  ready  for 
cupellation  with  the  regular  assay.  The  reason  for  making  up 
the  proof  in  this  manner  is  that  the  loss  of  silver  in  cupellation 
will  depend  upon  the  amount  of  lead  and  copper  present. 

The  pure  silver-foil  used  can  be  made  by  the  reduction  of 
the  silver  chloride  obtained  in  parting,  or  it  can  be  purchased 
from  dealers. 

The  regular  assay  is  performed  as  follows :  Two  portions 
of  bullion  weighing  0.500  gm.  each  are  accurately  weighed  out 
on  the  button-balance  and  wrapped  in  the  proper  amount  of 
lead-foil  as  shown  by  the  table.  The  lead-foil  can  be  cut  into 
sheets  of  the  proper  weight.  The  lead-foil  should  be  free 
from  silver ;  but,  if  it  contains  a  small  amount  of  silver  and  its 
silver  contents  are  uniform,  the  silver  which  it  contains  can  be 
disregarded,  as  the  same  amount  will  be  present  in  the  lead 
used  in  the  proof-assay.  The  proof  is  made  up  as  indicated 
above.  Have  three  hot  cupels  in  the  muffle  and  introduce 
into  each  one  of  the  assays,  placing  the  test-assay  in  the  middle. 
Proceed  with  the  cupellation  in  the  manner  described  under 
the  preliminary  assay,  taking  care  to  have  the  cupellation  of 
all  three  of  the  assays  start  and  finish  at  about  the  same  time ; 
that  is,  have  all  three  run  at  about  the  same  temperature. 
Weigh  -all  three  buttons :  the  loss  in  silver  of  the  test-assay 
will  represent  the  loss  in  cupellation.  In  the  case  of  fine 
bullion  this  loss  should  be  from  4  to  5  mgs.  If  greater  than 
5  mgs.,  the  assay  has  been  run  too  hot  or  too  cold.  The 
buttons  should  be  bright,  and  should  show  no  evidence  of 
litharge.  The  loss  in  the  test-assay  is  added  to  each  of  the 
regular  assays  when  the  product  of  the  two  assays  will  give  the 
fineness  of  the  bullion.  The  two  buttons  should  not  differ 
from  each  other  by  more  than  I  mg.  A  greater  difference, 
except  in  the  case  of  very  impure  bullion,  when  a  greater  num- 
ber of  assays  should  be  run,  should  not  be  allowed.  Suppose 
button  No.  i  weighs  489  mgs.,  button  No.  2  weighs  488  mgs., 
and  the  test  shows  a  loss  of  4.5  mgs. ;  then 

(489  +  4.5)  +  (488  +  4-5)  =  986  fine. 


240  A    MANUAL    OF  PRACTICAL   ASSAYING. 

The  buttons  are  parted  for  gold  (see  assay  of  Gold  Bullion, 
Part  III,  Chapter  III),  and  the  gold  fineness  is  deducted  from 
the  total  fineness  (Ag  and  Au)  to  determine  the  silver  fineness. 

Second  Method. — This  method  requires  the  following 
solutions  :  Normal-salt  solution,  decinormal-salt  solution,  and 
decinormal  solution  of  silver  nitrate. 

The  normal-salt  solution  is  a  solution  of  salt  in  water,  100 
cc.  of  which  will  precipitate  exactly  i.o  gm.  of  silver  as  silver 
chloride. 

The  decinormal-salt  solution  is  a  solution  of  salt  in  water,  one 
cc.  of  which  will  precipitate  exactly  i.o  mg.  of  silver.  This  solu- 
tion is  made  by  diluting  one  part  of  the  normal  solution  with 
nine  parts  of  water.  In  making  up  this  solution  care  should 
be  taken  to  have  the  temperature  of  the  solution  and  the  water 
used  for  dilution  the  same. 

The  decime-silver  solution  is  a  solution  of  pure  silver  in 
nitric  acid,  diluted  with  distilled  water.  One  cc.  of  this  solu- 
tion contains  i.o  milligramme  of  silver,  consequently  I  cc.  is 
equivalent  to  I  cc.  of  decime-salt  solution. 

To  prepare  the  normal-salt  solution  dissolve  5.4167  grammes 
of  pure  dry  sodium  chloride  (dried  by  heating  at  about  125°  C.) 
in  distilled  water,  and  dilute  to  1000  cc.  Where  many  assays 
are  to  be  made,  it  is  usual  to  prepare  a  greater  quantity  of  the 
solution,  the  above  being  given  simply  to  indicate  the  "amount 
of  salt  to  be  used.  In  making  up  and  measuring  the  solutions 
care  should  be  exercised  to  have  the  temperatures  remain  the 
same.  A  good  plan  in  making  up,  measuring,  and  standardiz- 
ing is  to  have  the  solutions  at  the  ordinary  temperature  of  the 
laboratory.  The  laboratory  in  which  the  solutions  are  kept 
and  the  assays  performed  should  have  a  nearly  constant  tem- 
perature. A  convenient  form  of  apparatus  in  which  to  keep 
the  solutions  is  a  carboy  or  large  glass  bottle,  provided  with  a 
rubber  stopper  perforated  with  two  holes.  Into  one  of  these 
holes  is  introduced  a  piece  of  glass  tubing  whose  lower  end 
reaches  nearly  to  the  bottom  of  the  flask.  In  the  other  hole 
introduce  a  piece  of  glass  tubing  bent  in  the  form  of  a  siphon, 
the  end  in  the  bottle  reaching  nearly  to  the  bottom,  whilst  the 


ASSAY  OF  SILVER  BULLIO 


other  end  is  a  foot  or  so  below  the  level  of  the  bottom  of  the 
bottle  and  a  convenient  height  above  the  work-table.  This 
siphon  tube  should  be  provided  with  a  stop-cock,  situated  at  a 
convenient  height,  and  a  piece  of  rubber  tubing  on  the  end,  the 
latter  being  provided  with  a  pinch-cock.  From  time  to  time 
the  solution  in  the  bottle  should  be  shaken,  and  it  should  be 
restandardized  every  few  weeks,  as,  no  matter  what  precautions 
are  taken,  its  strength  is  liable  to  change. 

The  decime-salt  solution  is  prepared  by  drawing  off  exactly 
100  cc.  of  the  normal  solution  and  diluting  it  to  1000  cc.  with 
distilled  water  of  the  same  temperature.  It  is  unnecessary  to 
prepare  a  large  quantity  of  this  solution,  as  it  can  be  readily 
prepared  from  time  to  time,  as  needed,  from  the  normal  solu- 
tion. 

The  decime-silver  solution  is  prepared  by  dissolving  i 
gramme  of  perfectly  pure  silver  in  a  few  cc.  of  dilute  nitric 
acid,  and  diluting  to  1000  cc.  It  is  best  to  prepare  this  solu- 
tion freshly  about  once  a  week,  and  it  should  be  kept  in  a 
green-glass  bottle  covered  with  black  paper,  and  provided  with 
a  siphon  for  convenience  in  drawing  off  into  the  burette. 

After  preparing  the  salt  solutions  they  must  be  carefully 
standardized  as  follows :  Three  or  four  portions  of  pure  silver 
of  exactly  I  gramme  each  are  weighed  out,  and  each  portion 
is  introduced  into  a  glass-stoppered  flask  of.  about  250  cc. 
capacity.  The  silver  in  each  flask  is  now  dissolved  in  10  cc.  of 
dilute  nitric  acid  (free  from  chlorine),  placing  the  flask  in  an 
inclined  position  on  the  sand-bath  to  facilitate  solution  and 
avoid  loss.  After  the  silver  is  all  dissolved  dilute  the  contents 
of  the  flask  with  about  80  cc.  of  distilled  water.  Run  into  a 
pipette  100  cc.  of  the  normal  solution,  and  add  the  solution 
from  the  pipette  to  the  contents  of  the  flask.  Close  the  flask 
with  the  stopper,  and  agitate  violently.  After  agitation  place 
the  flask  in  a  dark  place  (a  box  with  several  holes  in  the  top 
in  which  to  introduce  the  flasks  is  convenient),  and  allow  the 
precipitate  to  settle.  Repeat  the  agitation,  if  necessary,  until 
the  solution  settles  clear,  and  then  add  I  cc.  of  the  decime-salt 
(prepared  for  this  purpose  by  drawing  off  25  cc.  of  the  normal- 


242  A   MANUAL   OF  PRACTICAL  ASSAYING. 

salt  solution,  and  diluting  with  225  cc.  of  distilled  water)  solu- 
tion from  a  burette.  Should  a  precipitate  appear,  agitate  and 
allow  to  settle  as  before,  and  repeat  the  addition  of  decime-salt 
solution  until  a  precipitate  fails  to  appear.  The  solution  should 
be  added  slowly  at  first,  and  the  addition  stopped  as  soon  as  a 
precipitate  fails  to  appear.  The  reading  of  the  burette  is  now 
noted,  the  contents  of  the  flask  agitated  and  allowed  to  settle. 
The  decime  solution  of  silver  nitrate  is  now  added  from  a 
burette,  adding  not  more  than  I  cc.  at  a  time.  This  addition 
is  continued,  agitating,  and  allowing  the  contents  of  the  flask 
to  settle  after  each  addition  until  the  silver  nitrate  no  longer 
produces  a  precipitate,  when  the  reading  of  the  burette  is 
noted. 

The  method  of  calculation  is  best  illustrated  by  the  follow- 
ing examples: 

Suppose  100  cc.  of  the  normal  solution  was  insufficient  to 
precipitate  all  the  silver,  and  7  cc.  of  the  decime-salt  solution 
were  added.  Then  I  cc.  of  the  decime-silver  solution  is  added, 
resulting  in  the  formation  of  a  precipitate.  The  addition  of  a 
second  cc.  of  the  silver  solution  fails  to  produce  a  precipitate. 
Hence,  100.7  —  (.2  —  .1)  =  100.6  cc.  of  the  normal-salt  solution, 
which  is  necessary  to  precipitate  I  gramme  of  silver,  whilst  only 
100  cc.  should  be  required.  The  normal-salt  solution  is  conse- 
quently too  weak,  and  the  quantity  of  salt  to  be  added  to  1000 
cc.  may  be  calculated  as  follows : 

(100  —  0.6)  :  5.4167  ::  0.6  :  x. 
x  =  0.0327  grammes  of  NaCl. 

Suppose  100  cc.  of  the  normal-  and  I  cc.  of  the  decime-salt 
solution  were  added,  the  decime  solution  failing  to  produce  a 
precipitate.  Decime-silver  solution  was  then  added  to  the 
amount  of  8  cc.,  the  last  cc.  failing  to  produce  a  precipitate. 
Hence,  100.1  —  (.8  —  .1)  =  99.4  cc.,  required  to  precipitate  I 
gramme  of  silver,  whilst  100  cc.  should  be  required;  conse- 
quently the  solution  contains  an  excess  of  salt. 

i  :  0.006  ::  5.4167  :  x. 
x  =  salt  in  excess  =  0.0325002  gm. 


ASSAY  OF  SILVER  BULLION.  243 

The  following  calculation  gives  the  number  of  cc.  of  water 
to  add  to  each  1000  cc.  of  solution  in  order  to  make  it  normal: 

0.0325002  .. 

2-2- —  x  1000  =  6  cc. 

5.4167 

Salt  or  water  should  be  added  as  required,  the  solution 
being  thoroughly  mixed  and  restandardized.  This  operation 
is  to  be  repeated  until  the  solution  is  brought  to  the  normal 
point.  After  a  normal  solution  is  obtained  a  decime  solution 
can  be  made  by  diluting  100  cc.  of  the  normal  solution  with 
900  cc.  of  water. 

The  use  of  a  normal  solution  of  sodium  bromide,  rather 
than  sodium  chloride,  is  preferred  by  some  chemists  using  this 
method.  Sodium  bromide  is  preferable,  as  silver  bromide  is 
practically  insoluble  in  water  containing  a  slight  excess  of 
sodium  bromide,  whilst  silver  chloride  is  slightly  soluble  in 
water  containing  a  slight  excess  of  sodium  chloride.  If  sodium 
bromide  is  used,  9.5370  grammes  of  the  dried  salt  dissolved 
in  water  and  diluted  to  1000  cc.  should  produce  a  normal 
solution.  The  solution  is  standardized,  and  the  assay  per- 
formed in  the  same  manner  as  when  sodium  chloride  is  used. 

The  regular  assay  can  now  be  made  as  follows:  First  deter- 
mine the  approximate  fineness  of  the  bullion  by  cupellation,  as 
described  above,  or  by  weighing  out  0.5  gramme  of  the  bullion, 
solution  in  dilute  nitric  acid,  and  titration  with  the  standard 
salt  solution,  using  the  normal  solution  to  start  with,  and  the 
decime  solution  to  finish  with.  A  good  plan  is  to  pour  off  one 
half  of  the  solution  of  the  bullion  into  a  beaker,  and  approxi- 
mately determine  the  amount  of  silver  in  the  half  remaining  in 
the  flask.  Now  add  the  solution  in  the  beaker  to  the  flask, 
and  finish  the  titration.  •  In  this  manner  the  amount  of  normal- 
salt  solution  which  can  be  safely  added  is  determined,  and  the 
final  titration  with  the  decime  solution  is  quickly  proceeded 
with. 

Having  determined  the  fineness  approximately,  the  amount 
of  bullion  to  weigh  out  for  assay  (so  as  to  have  about  i  gramme 


244  A   MANUAL   OF  PRACTICAL  ASSAYING. 

of  silver  present  in  each  assay)  can  be  obtained  from  the  table. 
It  is  usual  to  take  at  least  two  portions  for  assay.  Dissolve 
each  portion  in  a  25<>cc.  stoppered  flask  with  dilute  c.  p.  nitric 
acid,  and  dilute  with  water  to  about  80  cc.  Add  100  cc.  of 
normal-salt  solution,  agitate,  and  proceed  as  above  described. 
The  method  of  calculating  results  is  best  illustrated  by  an 
example,  as  follows:  Suppose  we  have  taken  i.oi  gramme  of 
bullion,  and  have  used  100  cc.  of  the  normal-  and  1 1  cc.  of  the 
decime-salt  solution.  Having  added  too  much  salt  solution,  we 
add  2  cc.  of  the  decime-silver  solution,  and  titrate  again  with 
the  decime-salt  solution,  drop  by  drop,  using  0.5  cc.  altogether, 
when  a  precipitate  fails  to  appear. 

Salt  solution  used,  100  cc.  normal,       =  1000.00  mgs.  Ag. 
"          "  "      11.5  cc.  decime,       —       11.50      " 

1011.50  mgs.  Ag. 
Less  decime-silver  solution  used,  2  cc.,  t=        2.00      "       " 

1009.50  mgs.  Ag. 
If  x  =  fineness  in  thousandths,  we  have 

i.oi  :  1.0095  ::  1000  :  x. 

x  =  999.5. 

As  this  assay  cannot  be  made  in  a  laboratory  where  fumes 
of  chlorine,  bromine,  or  ammonia  are  present,  it  is  best  to  have 
a  separate  room  for  this  assay.  If  a  separate  room  is  used  it  is 
preferable  to  have  the  light  admitted  through  yellow  glass,  as 
the  rays  admitted  by  yellow  glass  do  not  decompose  chloride 
or  nitrate  of  silver.  Should  the  bullion  treated  contain  mer- 
cury, sunlight  will  not  blacken  the  precipitated  silver  chloride. 
Should  mercury  be  present,  it  may  be  held  in  solution  by  the 
addition  of  10  grammes  of  sodium  acetate  containing  a  few 
drops  of  free  acetic  acid. 

Should  the  bullion  contain  lead,  it  can  be  precipitated,  before 
titration  with  the  salt  solution,  by  the  addition  of  a  few  cc.  of 
sulphuric  acid. 


ASSAY  OF  SILVER  BULLION.  245 

Third  Method — Volhard's  method  gives  excellent  results 
on  bullion  free  from  copper,  but  cannot  be  used  for  the 
determination  of  silver  in  coin  or  bullion  containing  even  small 
amounts  of  copper.  It  consists  in  dissolving  the  bullion  in  a 
small  amount  of  nitric  acid,  as  in  the  second  method,  adding 
about  5  cc.  of  a  strong  solution  of  ferric  ammonium  sulphate 
as  an  indicator,  and  titrating  with  a  standard  solution  of 
potassium  sulphocyanide  in  the  manner  described  in  Part  II, 
Chapter  X,  page  145.  It  is  best  to  prepare  two  standard 
solutions  of  potassium  sulphocyanide — one  where  each  cc.  is 
equivalent  to  10  mgs.  of  silver,  and  a  decime  solution  each  cc. 
of  which  is  equal  to  I  mg.  of  silver.  The  titration  is  com- 
menced with  the  strong  solution,  and  is  finished  with  the 
decime  solution. 

The  normal  solution  may  be  prepared  by  adding  about  9 
grammes  of  potassium  sulphocyanide  to  the  litre  of  distilled 
water. 

The  author  has  frequently  used  this  method  for  the 
determination  of  the  fineness  of  Dore  bullion,  produced  by 
zinc  desilverization  and  cupellation,  and  for  such  material 
considers  it  as  rapid  and  accurate  as  any  method  which  we 
have. 


CHAPTER   III. 
THE  ASSAY  OF  GOLD  BULLION. 

THE  process  of  assaying,  which  is  essentially  one  of  refining, 
requires  the  removal  of  both  the  base  metals  and  the  silver. 
To  effect  this  two  operations  are  necessary : 

First.  The  base  metals  are  removed  by  cupellation.  Weigh 
out  0.500  gm.  on  a  delicate  balance,  wrap  in  5  gms.  of  pure 
sheet  lead,  and  cupel  (see  Chapter  II :  Assay  of  Silver  Bullion). 
Lead  under  the  action  of  the  heat  and  air  forms  litharge, 
which  dissolves  the  oxides  of  the  base  metals  and  carries  them 
into  the  cupel,  leaving  behind,  when  the  operation  is  completed, 
which  is  shown  by  the  brightening  of  the  button,  pure  silver 
and  gold.  The  button  of  silver  and  gold  is  weighed,  and  the 
difference  between  this  weight  and  the  0.500  gm.  taken  rep- 
resents the  weight  of  the  base  metal. 

Second.  The  silver  is  removed  from  the  gold  by  solution 
in  nitric  acid,  the  gold  remaining  behind  in  an  insoluble  state. 
In  order  that  the  silver  be  entirely  removed,  it  is  necessary 
that  there  be  present  at  least  twice  as  much  silver  as  gold. 
A  preliminary  assay  is  run  by  weighing  out  0.500  gm.  of 
bullion,  adding  i.o  gm.  of  pure  silver,*  wrapping  in  5  gms.  of 
sheet  lead,  and  cupelling.  The  resulting  button  is  detached 
from  the  cupel,  brushed  and  weighed,  and  then  flattened  out 
under  a  hammer,  the  weight  being  noted.  It  is  then  heated  to 
redness  in  a  clay  annealing-cup  and  passed  through  a  small  set 
of  rolls,  which  draw  it  out  to  about  4  inches  in  length.  It  is 
again  annealed,  and  when  cold  is  rolled  into  a  spiral  coil  called 
a  cornet.  It  is  now  ready  for  the  acid.  For  this  purpose  a 
platinum  dish  about  3  inches  in  diameter  and  2  inches  deep 

*  Unless  the  bullion  contains  copper  about  10  mgs.  of  pure  copper  is  also 
added  to  toughen  the  cornet. 

246 


THE  ASSAY  OF   GOLD  BULLION.  247 

is  used.  This  is  nearly  filled  with  c.  p.  nitric  acid  of  32° 
Baume"  and  heated  to  boiling.  The  cornets  are  placed  in  a 
small  platinum  crate,  with  a  separate  compartment  for  each 
cornet.  This  crate  is  now  lowered  into  the  boiling  acid  and 
allowed  to  boil  for  10  minutes,  as  shown  by  an  electric  indi- 
cator. The  acid  is  now  poured  off,  the  dish  filled  with  fresh 
acid  of  the  same  strength,  and  again  boiled  for  10  minutes. 
The  crate  containing  the  cornets  is  now  lifted  out  and  washed 
with  pure  distilled  water.  After  drying  slowly,  the  platinum 
crate  and  cornets  are  exposed  for  a  few  minutes  to  a  strong 
red  heat,  which  condenses  and  anneals  them.  When  cool,  the 
cornets  are  weighed  and  the  number  of  milligrammes  which 
they  weigh  is  noted.  Suppose  this  preliminary  assay  shows 
0.380  gm.  of  gold  and  o.oio  gm.  of  silver,  then  twice  0.380  = 
0.760,  and  0.760  —  5  (half  the  silver  present)  =  0.755  gm.  of 
silver,  which  it  is  necessary  to  add  to  the  regular  assay  in  order 
that  there  be  twice  as  much  silver  present  as  gold. 

For  the  regular  assay  0.500  gm.  of  bullion  is  weighed  out 
on  a  delicate  balance.  This  weight  is  marked  1000.  All  the 
lesser  weights  used  are  decimal  divisions  of  this  weight,  down 
to  one  ten-thousandth  part.  From  the  preliminary  assay  the 
amount  of  silver  necessary  to  add  is  calculated.  The  bullion 
and  the  added  silver  are  wrapped  in  5  gms.  of  sheet  lead  and 
cupelled,  the  regular  assay  being  performed  exactly  as  above. 
In  practice  it  is  not  general  to  take  as  much  care  with  the 
preliminary  assay  as  with  the  regular  assay. 

As  the  process  is  subject  to  error  from  a  number  of  causes, 
but  principally  owing  to  the  losses  of  the  precious  metals  from 
volatilization  and  absorption  while  on  the  cupel,  and  from  im- 
perfect extraction  of  the  silver  by  the  acid,  it  is  necessary  to 
make  a  test  assay  with  each  set  of  assays.  This  assay  is  made 
from  chemically  pure  gold,  and  is  made  up  as  nearly  like  the 
bullion  under  examination  as  possible.  This  is  passed  through 
the  same  processes  as  the  samples  of  bullion  under  assay,  and 
side  by  side  with  them.  It  is  evident  that,  ?f  the  process  were 
a  perfect  one,  we  would  recover  from  the  test-assay  exactly  the 
amount  of  gold  taken.  If,  however,  from  any  cause,  it  is  found 


248  A   MANUAL   OF  PRACTICAL  ASSAYING. 

to  differ  from  the  weight  taken,  and  therefore  found  to  require 
a  correction,  it  is  assumed  that  the  same  correction  should  be 
made  to  the  regular  assays ;  and  this  is  done.  The  weights  of 
the  cornets  with  this  correction  give  the  true  fineness  in  gold. 

The  gold  fineness  being  known,  and  also  the  fineness  in 
silver  and  gold,  the  silver  fineness  is  determined  by  difference. 
In  practice  the  fineness  of  unparted,  or  Dore,  bars  is  reported 
to  the  half-thousandth. 

While  the  method  as  described  is  essentially  that  adopted 
by  some  of  the  government  offices,  in  practice  the  author  uses 
the  following  modifications: 

A  preliminary  assay  is  seldom  necessary,  as  after  considera- 
ble experience  the  assayer  will  be  able  to  judge  very  approxi- 
mately the  fineness  of  the  bullion  by  simple  eye  inspection, 
and  from  the  manner  in  which  the  bullion  cuts  with  the  shears 
after  rolling  into  a  ribbon.  These  estimates  are  generally  suf- 
ficiently close  where  two  and  one  half  parts  of  silver  (to  one 
part  gold)  are  used  in  alloying.  Where  the  proportion  of  two 
to  one  is  adopted  a  preliminary  assay  is  necessary,  as  in  this 
case  so  wide  a  variation  is  not  permissible.  For  this  reason 
the  author  has  adopted  the  proportion  of  two  and  a  half  parts 
.silver  in  alloying. 

As  the  proportion  of  silver  to  gold  is  increased  the  strength 
of  the  first  acid  must  be  decreased.  Where  the  proportion 
of  two  and  one  half  is  adopted  the  first  acid  should  have  a 
strength  of  25°  Baume  (=  1.20  sp.  gr.).  The  cornets  are  boiled 
in  this  acid  until  all  action  of  the  acid  has  ceased.  This  gen- 
erally requires  about  ten  minutes'  boiling.  The  acid  is  now 
poured  off,  and  fresh  acid  of  32°  Baume  (—  1.27  sp.  gr.)  is 
added.  The  cornets  are  boiled  in  the  second  acid  for  exactly 
ten  minutes. 

Where  a  proof  or  blank  assay  is  run  with  each  set  of  assays 
(the  use  of  a  proof  has  been  generally  adopted)  care  should 
be  exercised  that  the  proof  is  run  under  exactly  the  same  con- 
ditions as  the  bullion  under  examination.  For  this  reason  the 
platinum  parting  apparatus  is  preferable  to  the  flasks.  Care 


THE  ASSAY  OF  GOLD  BULLION. 


249 


should  also  be  exercised  to  have  each  cornet  of  exactly  the 
same  thickness  after  passing  through  the  rolls. 

As  the  surcharge  of  silver  (silver  remaining  with  the  gold 
after  parting)  depends  upon  the  thickness  of  the  cornets,  the 
strength  of  the  first  and  second  acids  and  the  time  of  boiling, 
the  proportions  of  alloy,  the  strength  of  acid,  the  thickness  of 
cornets,  and  time  of  boiling  should  be  the  same  in  all  assays. 

The  correction  for  the  loss  of  silver  in  cupellation  of  the 
base-metal  assay  is  generally  made  by  running  a  proof  assay, 
the  proof  being  made  up  of  pure  gold  and  silver,  and  as  nearly 
like  the  bullion  under  examination  as  possible  (see  the  fire- 
assay  of  silver  bullion,  Part  III,  Chapter  II).  Where  gas  fur- 
naces are  used  for  cupelling  the  temperature  can  be  controlled 
within  quite  narrow  limits.  In  such  a  case  the  silver  losses 
may  be  determined  on  bullion  of  different  fineness,  and  corre- 
sponding corrections  can  be  made  in  subsequent  assays. 

The  following  table  gives  the  proportions  of  silver  and  lead 
used  by  the  author  for  the  gold  determination  on  the  average 
bullion  carrying  silver,  and  on  coppery  bullion  such  as  jewellers' 
melts : 


Ordinary  Bullion. 

Coppery  Bullion. 

Fineness. 

Add  Silver 
Mgs. 

Add  Lead 
Gms. 

Fineness. 

Add  Silver 
Mgs. 

Add  Lead 
Gms. 

Add  Lead  to 
Base-metal 
Assay,  Gms. 

500 

400 

5 

500 

5  50-600 

IO 

10 

550 

500 

5 

550 

650-700 

9 

9 

600 

575 

5 

600 

700-750 

8 

8 

650 

650 

5 

650 

750-800 

8 

8 

7OO 

750 

5 

700 

850 

7 

7 

750 

850 

5 

750 

950 

7 

7 

800 

925 

41 

800 

IOOO 

6 

6 

850 

1025 

4* 

850 

1050 

6 

6 

900 

IIOO 

4 

900 

1125 

5 

5i 

950 

"75 

4 

950 

1200 

4* 

5 

IOOO 

1250 

4 

IOOO 

1250 

4 

4 

For  the  base-metal  assay  of  ordinary  bullion  5  gms.  of  lead  is  used. 


CHAPTER   IV. 

SPECIAL  METHOD  FOR  THE  DETERMINATION  OF  SILVER 
AND   GOLD   IN   COPPER   MATTES,   ETC. 

IN  the  determination  of  silver  and  gold  in  copper  mattes, 
pig-copper,  and  ores  carrying  much  copper,  by  the  usual  method 
of  scorification-assay  the  losses  of  silver  and  gold  are  quite 
large,  usually  from  2  to  4  per  cent  of  the  silver  present  being 
lost,  owing  to  the  fact  that  in  order  to  obtain  lead  buttons 
which  are  soft  and  free  from  copper  repeated  scorifications  are 
necessary,  and,  moreover,  it  is  impossible  to  obtain  lead  but- 
tons which  are  entirely  free  from  copper.  If  the  lead  button 
contains  copper,  silver  will  be  carried  into  the  cupel  when  the 
button  is  cupelled. 

The  following  method  is  a  modification  of  the  method  of 
Prof.  Whitehead,*  and  is  believed  to  give  the  best  results  :f 

One  A.  T.  of  material  is  introduced  into  a  No.  5  beaker  and 
100  cc.  of  distilled  water  are  added,  stirring  the  mass  with  a 
glass  rod  ;  50  cc.  of  nitric  acid  (sp.  gr.  1.42)  are  added,  and  the 
solution  is  allowed  to  stand  until  the  action  of  the  acid  has 
apparently  ceased.  Then  50  cc.  more  acid  is  added,  and  the 
solution  is  allowed  to  stand  in  a  warm  place  until  the  red  fumes 
are  driven  off;  the  solution  is  now  diluted  with  distilled  water 
to  500  cc.,  and  allowed  to  stand  for  several  hours.  The  solu- 
tion is  now  filtered  off  through  a  rather  heavy  4^-inch  filter- 
paper,  the  water  used  in  transferring  the  precipitate  to  the  filter 
being  usually  sufficient  to  remove  the  copper  and  silver  salts. 
To  the  clear  solution  normal  sodium-chloride  solution  (i  cc.  = 
10  mgms.  silver)  is  now  added  in  slight  excess.  A  large  excess 

*  Journal  of  Analytical  and  Applied  Chemistry,  Vol.  VI,  p.  262. 
f  Dr.  Le  Doux's  paper  on  the  Assay  of  Copper  and  Copper  Mattes.     Results 
and  Discussion.     Trans,  of  the  Am.  Inst.  of  Mining  Engineers,  1894  and  1895. 

250 


SILVER  AND   GOLD   IN  COPPER  MATTES,   ETC.         2$ I 

is  to  be  avoided,  as  silver  chloride  is  soluble  in  an  excess  of 
salt.  The  solution  is  stirred  and  10  cc.  of  a  saturated  solution 
of  lead  acetate  are  added,  with  stirring  of  the  solution.  Then 
2  cc.  of  sulphuric  acid  (i  part  acid  to  i  part  water)  are  added, 
and  after  stirring  the  solution  is  allowed  to  stand  for  a  few 
hours.  When  the  precipitate  has  settled  the  solution  is  filtered 
off  and  the  precipitate  is  washed  into  the  filter,  finally  washing 
the  precipitate  to  remove  copper  salts.  The  filtrate  should  be 
perfectly  clear.  The  filters  are  removed  from  the  funnels,  and 
after  wrapping  them  around  the  precipitates,  are  placed  in  2j- 
inch  scorifiers  and  dried  by  placing  the  scorifiers  on  a  hot  plate. 
When  dry  the  papers  are  burned  by  placing  the  scorifiers  in 
front  of  the  muffle,  the  scorifiers  finally  being  pushed  back 
into  the  muffle  to  destroy  all  the  carbon  and  sulphur.  To 
scorifier,  containing  the  gold  residue  and  the  silver-lead  pre- 
cipitate, is  added  5  gms.  of  litharge,  15  to  20  gms.  of  test-lead, 
and  i  gm.  of  borax  glass.  The  charges  are  now  scorified  at  a 
moderate  temperature,  and  when  the  scorifications  are  finished 
are  poured.  The  lead  buttons,  which  should  weigh  from  6  to 
8  gms.  each,  are  cupelled  so  as  to  show  feather  litharge,  and 
the  gold-silver  buttons  are  weighed.  The  buttons  are  then 
flattened  and  parted  for  gold  in  the  usual  manner.  The  assay 
is  usually  run  in  duplicate,  and  the  two  results  should  agree 
almost  exactly. 

This  method  may  also  be  used  to  advantage  for  the 
determination  of  gold  and  silver  in  base  ores,  as  gray  copper, 
arsenical  sulphides,  etc.  The  method  may  also  be  used  for  the 
assay  of  silver  sulphides  and,  in  the  opinion  of  the  author,  is 
preferable  to  that  described  on  page  252.* 

*  Trans,  of  the  Am.  Inst.  of  Mining  Engineers,  1895. 


CHAPTER  V. 
ASSAY  OF  SILVER  SULPHIDES. 

IN  the  ordinary  crucible-assay  of  precipitated  silver  sul- 
phides from  a  leaching-works  the  loss  of  silver  in  the  slag  and 
in  the  cupel  will  vary  from  0.2  to  1.5  per  cent.  There  is  also  an 
additional  loss  by  volatilization  during  fusion  and  cupellation.* 
The  loss  in  scorification  will  vary  from  0.8  to  1.5  per  cent,  in 
addition  to  the  usual  loss  by  volatilization.  These  losses  were 
determined  in  the  case  of  high-grade  (11,000  to  12,000  ounces 
silver  per  ton)  sulphides.  In  the  case  of  low-grade  sulphides 
carrying  considerable  copper  the  losses  will  be  greater.  Scori- 
fication-assay  gives  the  best  results. 

In  consequence  of  this  loss  it  is  usual  to  determine  the 
silver  in  these  sulphides  by  "  corrected  assay."  From  six  to 
twenty  scorification-charges  are  run  on  each  lot  of  sulphides, 
using  the  following  charge:  Sulphides,  o.i  A.  T.,  test-lead  55 
gms.,  and  borax-glass  5  gms.  The  lead  buttons  are  extracted 
from  the  slag,  which  is  retained,  and  cupelled  separately.  The 
silver  buttons  are  weighed  and  their  average  taken  as  the 
result,  the  cupels  being  retained. 

The  slag  is  pulverized,  passed  through  a  2O-mesh  screen,  and 
assayed  by  crucible-assay  using  the  following  charge :  Slag ; 
litharge  20  gms. ;  sodium  carbonate,  15  gms.;  argol,  2  gms.; 
salt  cover.  The  resulting  lead  buttons  are  cupelled,  the  silver 
buttons  are  weighed  and  their  average  is  taken. 

The  cupels  are  pulverized,  passed  through  a  3O-mesh  screen 

*  Transactions  of  the  American  Institute  of  Mining  Engineers,  Vol.  XVI, 
page  378. 

252 


ASSAY  OF  SILVER   SULPHIDES.  2$ 3 

and  assayed  by  crucible-assay  using  the  following  charge : 
Cupel ;  litharge,  30  gms. ;  borax-glass,  30  gms.;  sodium  carbon- 
ate, 30  gms. ;  argol,  2  gms. ;  salt  cover.  The  resulting  lead 
buttons  are  cupelled,  the  silver  buttons  being  weighed  and  their 
average  taken. 

The  average  amount  of  silver  recovered  from  the  slag  and 
cupel  in  this  manner  is  added  to  the  average  amount  obtained 
by  the  first  scorification-assay,  the  result  being  the  corrected 
assay. 

The  gold  is  determined  by  treating  from  i  A.  T.  to  4  A.  T., 
in  a  beaker,  with  nitric  acid,  and  proceeding  in  the  manner 
described  in  Part  III,  Chapter  IV. 


CHAPTER    VI. 
CHLORINATION-ASSAY  OF  SILVER  ORES. 

IN  milling  silver  ores  by  the  Pan-Amalgamation  process 
chlorination-assays  are  made  daily  to  determine  the  per  cent 
of  chloride  of  silver  in  the  pulp.  These  assays  are  also  made 
as  a  check  on  the  process  in  a  leaching-works. 

The  process  requires  a  solution  of  hyposulphite  of  soda  con- 
taining two  pounds  of  hyposulphite  to  the  gallon  of  water,  and 
a  solution  of  sodium  sulphide. 

Weigh  out  two  samples  of  the  chloridized  pulp  of  from  y1^ 
A.  T.  to  £  A.  T.,  according  to  the  grade  of  the  ore.  Scorify 
one  with  about  30  gms.  of  test-lead  for  every  -^  A.  T.  taken, 
and  cupel.  Place  the  second  sample  in  a  beaker  and  add  some 
of  the  hyposulphite  solution.  Warm,  and  decant  on  a  filter* 
Continue  to  wash  with  the  hyposulphite,  finally  washing  the 
contents  of  the  beaker  onto  the  filter,  until  all  the  chloride  of 
silver  has  been  dissolved  and  leached  out  of  the  pulp.  This 
can  be  determined  by  testing  the  filtrate  from  time  to  time  with 
a  drop  of  the  sodium-sulphide  solution.  When  a  black  precipi- 
tate or  brown  coloration  no  longer  forms,  the  silver  chloride  is 
all  dissolved  and  the  desired  point  is  reached.  Wash  the  pulp 
on  the  filter  with  warm  water,  dry,  and  burn  the  filter  and  its 
contents  in  a  scorifier  in  the  muffle.  Mix  the  ashes  with  30  gms. 
of  test  lead  (for  each  y1^  A.  T.  taken)  and  scorify.  Cupel  the 
resulting  lead  button.  Having  the  assay  of  the  pulp  before 
and  after  leaching,  the  percentage  of  chlorination  is  arrived  at 
as  follows : 

Pulp-assays  before  leaching 95.00  oz.  Ag. 

Pulp-assays  after  leaching 9.00  oz.  Ag. 

254 


CHLORINATION-ASSAY  OF  SILVER   ORES. 

Hence,  if  x  =  per  ceht  of  silver  chloride, 

95  :  (95  -  9)  :  :  IO°  :  *• 
x  =  90.5. 

If  the  pulp  contains  sulphate  of  silver,  the  per  cent  of  sul 
phate  present  can  be  determined  by  weighing  out  a  third  sampla 
and  leaching  it  with  warm  water  until  all  the  silver  sulphate  is 
dissolved.  Dry,  burn,  scorify,  and  cupel  the  residue.  A  calcu- 
lation similar  to  the  above  will  give  the  percentage  of  silver 
present  as  sulphate.  To  determine  the  percentage  present  as 
chloride  deduct  this  per  cent  of  sulphate  from  the  per  cent 
obtained  by  leaching  with  the  hyposulphite  solution. 

To  determine  the  per  cent  of  silver  which  will  be  extracted 
by  the  Russel  Process  of  Lixiviation,  see  Trans,  of  the  Ameri- 
can Institute  of  Mining  Engineers,  Vol.  XVI,  pages  368-381. 
Also,  "  The  Lixiviation  of  Silver  Ores,"  by  C.  A.  Stetafeldt 
(Scientific  Pub.  Co.). 


CHAPTER  VII. 
CHLORINATION-ASSAY  OF  GOLD  ORES. 

A  CHLORINATION-ASSAY  of  a  gold  ore  is  made  to  determine 
the  probable  percentage  of  gold  which  may  be  extracted  by 
the  chlorination  process. 

The  percentage  of  extraction  will  depend  not  only  upon 
the  per  cent  of  free  gold  present,  but  also  upon  the  fineness  to 
to  which  the  ore  is  pulverized,  the  amount  of  chlorine  gas  gen- 
erated per  ore  charge,  and  the  time  of  agitation.  Hence  in 
treating  a  new  ore  a  series  of  tests  under  different  conditions 
will  be  required. 

The  general  practice  in  a  chlorination-mill  is  to  pulverize 
the  ore  to  about  40  mesh,  and  treat  in  a  closed  vessel  with 
bleaching-powder  and  sulphuric  acid.  The  sulphuric  acid  re- 
acts upon  the  bleaching-powder  and  chlorine  gas  and  calcium 
sulphate  are  produced.  (See  Part  III,  Chapter  XIV.)  The 
amount  of  bleaching-powder  used  per  ton  of  ore  in  the  mill 
will  vary  from  about  10  pounds  to  60  pounds.  The  amount  of 
sulphuric  acid  (66°  Baume)  used  will  vary  from  about  15  pounds 
to  70  pounds  per  ton  of  ore.  The  same  ratios  should  be  pre- 
served in  the  laboratory  tests. 

A  convenient  piece  of  apparatus  for  the  laboratory  test  is 
a  glass-stoppered  bottle  holding  from  one  to  three  gallons. 
From  one  to  ten  pounds  of  the  ore  is  weighed  out  and  intro- 
duced into  the  bottle.  The  proper  amount  of  warm  water  is 
added,  the  contents  of  the  bottle  agitated,  and  the  proper 
quantity  of  bleaching-powder  is  added.  The  proper  quantity 
of  sulphuric  acid  is  now  added,  the  bottle  is  tightly  stoppered, 
and  its  contents  agitated  from  four  to  eight  hours.  It  is  gen- 
erally best  to  add  a  portion  of  the  bleaching-powder  and 
sulphuric  acid  at  first,  agitate  for  from  three  to  five  hours,  and 
then  add  the  balance.  In  order  to  insure  perfect  chlorination 

256 


CHLORINATION-ASSAY  OF  GOLD    ORES. 

there  should  always  be  free  chlorine  present  at  the  last  of  the 
operation.  This  may  be  determined  by  removing  the  stopper 
and  holding  a  bottle  of  ammonia-water  to  the  mouth  of  the 
bottle.  If  free  chlorine  is  present  the  characteristic  fumes  of 
ammonium  chloride  will  be  produced. 

The  pulp  is  now  ready  for  filtration  and  washing,  which  is 
performed  in  the  usual  way.  When  the  washings  no  longer 
give  a  reaction  for  chlorine,  upon  testing  with  silver-nitrate 
splution,  the  washing  is  finished.  The  pulp  is  now  dried, 
sampled,  and  assayed  for  gold  in  the  usual  way. 

Having  the  assay  on  the  ore  before  and  after  treatment, 
the  following  gives  the  percentage  of  extraction  :  Suppose  the 
ore  before  treatment  assayed  0.77  oz.  Au,  and  after-treatment 
0.04  oz.  An  per  ton  of  2000  pounds.  Then 

0.77  —  0.04  =  0.73  —  gold  extracted,   and   0.77  :  0.73  :  :  100  :  x- 
x  =  94.8  =  percentage  of  extraction. 

Sulphides  must  be  roasted  previous  to  treatment.  Tk> 
roasting  must  be  carefully  conducted,  and  the  ore  finely 
brought  to  a  dead-roast,  in  order  to  insure  a  good  percentage 
of  extraction.  The  roasted  ore  should  not  show  much  ;.»ver 
0.3  per  cent  of  sulphur. 

The  following  table  gives  the  amount  in  grammes  of  b*;ach- 
ing-powder  or  sulphuric  acid  which  correspond  to  the  pounds 
per  ton  used  in  the  mill  : 

3.4    gms.  to  I  Ib.  is  equivalent  to  15  Ibs.  per  tcv. 
4.54     "      "      "     "          "  "  20    "      "      <s 

*  ^«     «       «      «     «  «  «  2c     «      <<       * 

6.80  "  "  "  "  "  "  30  "  "  '* 

704.  "  "  "  "  "  "    3^  tf  "  '< 

9.07  "  "  "  "  "  "  40  "  "  " 

IO  21  "  "  '*  u  **  "   AZ  "  "  " 


12  ^7  it  ii  «  (t  "  tt  H  H   « 

13.61  "  "  "  "  "  "  60  " 

14.74  ."  "  "  "  "  "  65 

1^.88  u  *'  "  "  "  "  70 


" 


CHAPTER  VIII. 

ASSAY  OF  GOLD  AND  SILVER  ORES  CONTAINING 
METALLIC  SCALES. 

IF  an  ore  of  gold  or  silver  contains  coarse  metallic  particles 
the  sample  will  consist  of  pulp  which  has  passed  through  the 
sieve  and  of  metallic  scales  which  remain  on  the  sieve. 

The  pulp  is  weighed  (preferably  in  grammes)  and  its  assay 
value  in  gold  and  silver  determined  in  the  regular  manner, 
either  by  scorification  or  crucible-assay.  The  scales  are  also 
weighed  (preferably  in  grammes)  and  their  assay  value  in  gold 
and  silver  is  determined  by  scorification-  or  crucible-assay. 
If  the  sample  of  scales  is  not  large,  the  whole  is  taken  for  assay. 
If  too  large,  an  aliquot  portion  is  carefully  taken  from  the 
sample  for  assay. 

The  results  may  be  calculated  in  the  same  manner  as  in  the 
assay  of  base  bullion  (see  Part  III,  Chap.  I),  or  they  may  be 
calculated  by  the  following  formula  :* 

Let  A  =  the  weight  of  the  pulp  in  grammes  ; 
B  =  the  weight  of  the  scales  in  grammes  ; 
C=  the  assay  value  of  the  pulp  in  ounces  of  gold  or 

silver  per  ton  of  2000  pounds  ; 

D  =  the  total  number  of  milligrammes  of  gold  or  silver 
in  the  scales. 

A 

Now  -  —  =  the  number  of  assay-tons  in  the  pulp  ;  and 
=  the  number  of  milligrammes  of  gold  or  silver  in  the 


*  State  School  of  Mines  Scientific  Quarterly,  Vol.  I,  No.  2,  Sept.  1892. 

258 


ASSAY  OF  GOLD   AND   SILVER   ORES.  2 59 

AC 
Hence, —  -f-  D  =  the  number  of  milligrammes  of  gold 

or  silver  in  the  whole  sample. 

Now  if  we  divide  the  total  number  of  milligrammes  of  gold 
or  silver  in  the  whole  sample  by  the  total  number  of  assay-tons 
in  the  whole  sample,  we  will  have  the  assay  value  of  the  whole 
sample  in  ounces  per  ton  of  2000  pounds.  The  expresssion 

A  -j-  B 

— — —  equals  the  total   number  of   assay-tons  in  the  whole 

29.166 

sample.     Hence,  making  the  division,  we  obtain  the  following 
formula  for  the  assay  value  of  the  whole  sample : 

A  C  +29.166/7 
A+B 

EXAMPLE. — Suppose  the  pulp  weighed  105.23  gms.  The 
scales  weighed  8.135  gms.  One  A.T.  of  the  pulp  yielded  10.5 
mgs.  of  Ag  and  28.3  mgs.  Au.  One  gramme  of  the  scales  upon 
assay  yielded  215.5  rngs.  Ag  and  682.5  mgs.  Au.  Now  the 
total  number  of  milligrammes  of  Ag  in  the  scales  equals 

8.135  X 

I 

and 


In  like  manner  we  obtain  for  the  assay  value  of  the  sample 
in  gold  per  ton  1454.68  ounces. 


CHAPTER   IX. 
AMALGAMATION-ASSAY. 

THE  amalgamation-assay  of  gold  and  silver  ores  is  some- 
times made  to  determine  the  probable  per  cent  of  the  gold  and 
silver  in  the  ore  which  can  be  extracted  by  amalgamation.  Like- 
all  laboratory  tests,  where  only  small  quantities  can  be  taken, 
the  results  will  simply  serve  as  a  guide  to  show  what  may 
probably  be  expected  on  a  commercial  scale  in  the  mill. 

Gold  Ores. — Pulverize  about  three  pounds  of  the  ore  and 
pass  through  an  So-mesh  sieve.  Sample  carefully  and  assay  the 
sample.  Weigh  out  from  one  to  three  pounds  of  the  pulverized 
ore  and  wash  by  panning  in  the  gold  pan.  The  ordinary  gold 
pan  is  a  shallow  sheet-iron  pan  15  inches  in  diameter  across 
the  top,  II  inches  in  diameter  on  the  bottom,  and  2  inches 
high.  The  ore  is  placed  in  the  pan  with  water,  and  panned 
by  giving  the  pan  a  vibratory  motion  as  in  vanning,  the 
light  particles  being  washed  over  the  sides.  An  expert  panner 
usually  performs  the  operation  under  water.  When  all  the 
light  particles  of  gangue  have  been  washed  off,  leaving  only 
the  gold  and  heavy  material  (as  black  sand)  in  the  pan,  the 
contents  of  the  pan  are  washed  into  a  wide-necked  flask  or 
bottle  and  a  few  ounces  of  mercury  added.  A  cork  or  stopper 
is  fitted  in  the  neck  of  the  flask  and  the  contents  agitated. 
It  is  best  to  use  boiling  water  in  the  flask,  as  heat  assists 
the  amalgamation.  The  pulp  and  mercury  in  the  flask  are 
agitated  several  times  when  the  contents  of  the  flasks  are 
poured  off,  except  the  mercury  and  amalgam,  and  washed 
several  times  with  water.  The  contents  of  the  flask  are  finally 
washed  out  into  the  gold  pan  and  the  mercury  and  amalgam 
further  freed  from  particles  of  ore  by  panning.  The  clean 

260 


A  MA  L  GA  MA  TION-A  SSA  Y.  26 1 

mercury  and  amalgam  are  now  strained  through  a  clean,  tight 
piece  of  buckskin,  when  the  amalgam  will  be  left  behind  in  the 
skin,  the  mercury  passing  through.  This  amalgam  is  collected 
in  a  small  porcelain  crucible  and  heated,  gradually  at  first,  to 
drive  off  the  mercury,  finally  heating  to  redness.  It  is  now 
cooled,  wrapped  in  a  piece  of  sheet  lead,  cupelled,  and  the  re- 
sulting button  weighed.  The  weighed  button  is  alloyed  with 
silver,  and  parted  as  in  the  assay  of  gold  bullion.  (See  Part 
III,  Chapter  III.) 

The  calculation  of  results  is  as  follows:  Suppose  the  ore 
assayed  i.o  oz.  gold  and  2  oz.  silver  per  ton.  The  button 
from  amalgamation  weighed  18  milligrammes.  After  parting, 
the  button  of  gold  weighed  12  milligrammes.  Hence  the  button 
contained  6  milligrammes  of  silver.  As  we  saved  12  mgs.  of 
gold  and  6  mgs.  of  silver  from  one  pound,  we  would  have  saved 
24  grammes  of  gold  and  12  grammes  of  silver  if  one  ton  of  ore 
were  used.  As  there  are  31.1035  grammes  in  one  ounce  Troy, 
we  have 

*y  A 

—  0.7716  oz.  of  gold  saved  per  ton, 


31-1035 
and 

12 
31-1035 


=  0.3858  oz.  of  silver  saved  per  ton. 


Let  x  =  per  cent  of  gold  saved  and  y  =  per  cent  of  silver 
saved.     Then 

i.o  :  0.7716  : :  100  :  x .    x  =  77.16$. 
2.0  :  0.3858  : :  100  :  y  .    y  —  19.29$. 

Silver  Ores. — From  one  to  three  pounds  of  the  ore  are 

pulverized,  sampled,  and  assayed  as  before.  One.  to  three 
pounds  are  weighed  out  and  placed  in  a  small  laboratory 
grinding-pan  together  with  hot  water.  The  pulp  in  the  pan  is 
then  ground  from  one  to  three  hours.  As  copper  sulphate 
and  salt  frequently  assist  the  amalgamation  on  some  ores,  they 
can  be  added  in  from  0.5  to  5.0  grammes  of  each.  A  few 


262  A    MANUAL    OF  PRACTICAL  ASSAYING. 

ounces  of  mercury  (according  to  the  amount  of  silver  in  the 
ore)  are  added  with  the  pulp.  After  the  grinding  is  finished 
the  contents  of  the  pan  are  agitated  with  water  and  the  pulp 
drawn  off,  the  final  washing  being  performed  in  the  gold  pan 
as  before  described.  The  amalgam  is  collected  and  treated  as 
before,  the  calculations  being  as  above. 

Another  method,  and  the  one  which  the  writer  prefers,  is 
to  have  a  small  pan,  similar  to  the  gold  pan  but  only  about  8 
inches  in  diameter,  made  from  sheet  copper.  The  bottom  and 
sides  of  this  pan  are  then  covered  with  a  coating  of  amalgam. 
A  few  ounces  of  the  finely  pulverized  ore  are  introduced  into 
the  pan,  the  mass  thinned  with  water,  and  the  pulp  thoroughly 
stirred  from  I  to  3  hours  with  a  wooden  stick  rounded  on  the 
end,  so  as  to  bring  all  particles  of  the  pulp  in  contact  with  the 
amalgamated  surface  of  the  pan.  The  pulp  is  now  poured  off 
on  to  a  filter,  and  all  the  pulp  remaining  in  the  pan  washed 
on  to  the  filter  with  the  aid  of  a  wash-bottle.  The  filter  and 
its  contents  having  been  thoroughly  dried,  the  pulp  is  sampled 
and  assayed.  The  difference  between  the  original  assay  of  the 
ore  and  the  assay  of  the  tailings  will  be  the  silver  and  gold 
which  has  been  collected  by  the  amalgamated  surface  of  the 
.pan,  or  the  silver  and  gold  in  the  ore  which  can  be  saved  by 
amalgamation.  Copper  pans  the  same  size  and  shape  as  the 
gold  pan  can  also  be  obtained.  It  is  only  necessary  to  amal- 
gamate the  sides  of  the  pan  for  a  short  distance  above  the 
bottom. 


CHAPTER   X. 
ANALYSIS  OF  COAL  AND   COKE. 

MINERAL  coal  is  made  up  of  different  kinds  of  hydrocar- 
bons, with,  perhaps,  in  some  cases,  free  carbon.*  Mineral 
coals  may  be  classified  as  follows,  according  to  H.  M. 
Chance  :f 

Anthracite — Volatile  matter  is  usually  less  than        7  p.  c. 
Semi-anthracite    "  "        "        "  "       "          10     " 

Semi-bituminous  "  "        "        "  "       "          18     " 

Bituminous — Volatile  matter  is  usually  more  than  18     " 

To  this  classification  should  be  added  the  lignites,  or  brown 
coals,  which  carry  a  high  percentage  of  water,  and  in  which  the 
percentage  of  volatile  matter  is  always  greater  than  18. 

For  practical  purposes,  an  approximate  analysis,  which 
consists  in  the  determination  of  moisture,  volatile  combustible 
matter,  fixed  carbon,  sulphur,  and  ash,  is  all  that  is  required. 
In  the  analysis  of  coke  all  that  is  usually  required  is  the  mois- 
ture, ash,  and  sulphur. 

Approximate  Analysis. — Determination  of  the  Moisture.— 
One  gramme  of  finely  pulverized  coal  is  introduced  into  a 
previously  weighed  platinum  crucible  and  dried  in  an  air-bath 
at  a  temperature  of  115°  C.,  until  the  weight  remains  constant 
or  begins  to  increase  owing  to  the  incipient  oxidation  of  the 
finely  divided  iron  pyrites.  The  last  lowest  weight  is  taken, 
and  the  loss  equals  moisture. 

Determination  of  the  Volatile  Matter. — Heat  the  crucible 
and  its  contents,  after  having  determined  the  moisture,  over 
the  flame  of  a  Bunsen  burner,  gradually  raising  the  temperature 

*  Dana's  System  of  Mineralogy,  Ed.  of  1885,  P-  754- 
f  Geological  Survey  of  Pennsylvania,  1888. 

263 


264  A   MANUAL   OF  PRACTICAL  ASSAYING. 

and  keeping  the  crucible  closely  covered  to  avoid  loss  by  finely 
divided  particles  of  carbon  being  carried  off  mechanically. 
Continue  this  heating  until  all  of  the  light  combustible  matter 
is  expelled.  This  will  require  4  to  5  minutes'  heating.  Now 
place  the  crucible  over  the  flame  of  a  blast-lamp  and  gradually 
raise  the  temperature  to  a  bright  red,  and  continue  the  heat  to- 
constant  weight  or  until  all  of  the  volatile  matter  is  expelled. 
This  heating  will  usually  take  about  10  minutes,  and  should  be 
carefully  conducted  in  order  to  avoid  loss  mechanically,  and 
should  not  be  unduly  prolonged,  as  this  would  involve  loss  of 
fixed  carbon  by  oxidation.  A  little  experience  will  teach  the 
assayer  when  the  operation  is  finished,  so  that  not  more  than. 
two  or  three  weighings  need  be  made.  Cool  the  crucible  and 
its  contents  in  a  desiccator,  and  weigh.  The  loss  equals  volatile 
matter  +  J  the  sulphur. 

Determination  of  the  Fixed  Carbon  and  Ash. — Heat  the 
crucible  and  its  contents,  after  having  expelled  the  moisture 
and  volatile  matter,  over  the  flame  of  a  blast-lamp  or  in  the 
muffle-furnace  at  a  gradually  increasing  temperature,  until  all 
of  the  carbon  is  oxidized  and  expelled.  It  is  best  to  heat  for 
half  an  hour  and  weigh.  Heat  for  10  minutes  and  weigh 
again,  repeating  this  operation  until  the  weight  remains  con- 
stant. After  a  little  experience  two  weighings  will  generally 
be  sufficient,  the  second  being  found  to  correspond  to  the 
first.  Loss  equals  fixed  carbon  and  half  the  sulphur,  and  the 
final  weight,  less  the  known  weight  of  the  crucible,  equals  ash. 

Whilst  this  analysis  is  at  best  an  approximation,  especially 
as  regards  the  determination  of  volatile  matter  and  fixed  car- 
bon, it  will  be  found  that  after  a  little  practice  it  will  give  a 
very  close  approximation  to  the  truth,  and  duplicate  analyses 
made  on  the  same  sample  will  agree  almost  exactly. 

The  supposition  that  half  of  the  sulphur  is  expelled  with  the 
volatile  matter  and  that  half  is  expelled  with  the  fixed  carbon 
is  based  upon  the  supposition  that  all  of  it  is  in  the  form  of 
iron  pyrites.  Of  course  this  supposition  would  be  almost 
universally  wrong,  but;  however,  for  practical  purposes  it 
answers  all  requirements,  especially  in  a  coal  low  in  sulphur* 


ANALYSIS  OF   COAL   AND    COKE.  26$ 

In  any  case  the  supposition  would  be  wrong,  as,  should  all  of 
the  sulphur  exist  in  the  form  of  iron  pyrites,  it  is  extremely 
improbable  that  half  would  be  expelled  in  the  treatment  given 
to  drive  off  the  volatile  matter.  For  practical  purposes  it  may 
generally  be  considered  that  half  of  the  sulphur  in  the  form  of 
pyrites  is  driven  off  with  the  volatile  matter  and  the  other  half 
with  the  fixed  carbon. 

If  it  is  necessary  to  determine  the  sulphur  which  exists  in 
the  coal  as  calcium  sulphate  and  pyrites,  it  may  be  done  as 
follows :  Determine  the  -total  sulphur  by  heating  2  to  5 
grammes  of  coal  with  nitric  acid  and  potassium  chlorate,  or 
by  fusion  with  caustic  potash  (see  Part  II,  Chapter  II),  evap- 
orating to  dryness,  after  addition  of  hydrochloric  acid  and 
previous  addition  of  bromine  in  the  case  of  fusion,  boiling  with 
water  and  hydrochloric  acid,  filtering,  washing,  and  the  addi- 
tion of  barium  chloride  to  the  filtrate. 

The  sulphur  existing  as  calcium  sulphate  may  be  deter- 
mined by  boiling  5  grammes  of  pulverized  coal  with  a  solution 
containing  about  5  grammes  of  c.  p.  sodium  carbonate  (free 
from  S),  thus  decomposing  the  calcium  sulphate  into  sodium 
sulphate  and  calcium  carbonate.  Filter  the  solution,  wash 
thoroughly  with  warm  water,  acidify  the  filtrate  with  hydro- 
chloric acid,  and  determine  sulphur  as  usual.  The  difference 
between  the  total  amount  of  sulphur  and  the  sulphur  found 
after  boiling  with  sodium  carbonate  (S  as  CaSO4)  represents 
the  amount  as  pyrites.  The  same  process  is  applicable  to  the 
determination  of  iron  sulphide  and  gypsum  in  coke. 

Any  phosphorus  which  the  coal  may  contain  will  be  in  the 
ash.  If  required,  determine  it  according  to  Part  II,  Chapter 
III.  If  determined,  deduct  it  from  the  ash  in  the  report. 

The  manner  of  tabulating  and  calculating  results  is  best 
illustrated  by  an  example  as  follows: 

Moisture 1.5 

Volatile  matter  -|-  J-  sulphur 27.5 

Fixed  carbon  -j-  J  sulphur 61.3 

Ash,  including  phosphorus 9.7 

Sulphur i.o 


266  A    MANUAL    OF  PRACTICAL  ASSAYING. 

When  the  sulphur  is  determined,  if  we  deduct  half  from  the 
volatile  matter  and  half  from  the  fixed  carbon,  the  report  would 
be  as  follows: 

Moisture 1-5° 

Volatile  matter 27.00 

Fixed  carbon 60.80 

Ash,  including  phosphorus. 9.70 

Sulphur i.oo 

100.00 

Determination  of  the  Specific  Gravity. — The  specific  gravity 
of  a  coal  is  often  required.  Take  a  small  piece  of  coal  and 
weigh  it  on  the  balance,  then  in  water  by  suspending  it  from 
the  arm  of  the  balance  by  a  hair  or  thin  wire.  The  piece 
taken  should  not  be  too  small,  and  care  should  be  taken  that 
no  air-bubbles  adhere  to  it  during  the  weighing.  The  coal 
also  should  be  thoroughly  soaked,  which  can  be  attained  by 
immersing  the  lump,  after  attaching  the  hair  or  wire  to  it,  in 
the  flask  of  the  filter-pump,  and  exhausting  the  air  in  the 
apparatus.  The  temperature  of  the  air  and  water  should  be 
the  same,  about  60°  F. 

Let  W  =  the  weight  of  the  coal  in  air ; 
W  =  the  weight  of  the  coal  in  water. 

W 
The  specific  gravity  ==  y^_  w,- 

Determination  of  the  Heating  Power. — This  determination 
is  sometimes  required,  but  at  the  most  is  simply  an  approxi- 
mation. Knowing  the  elementary  constitution  of  the  fuel,  the 
heating  power  may  be  tested  by  determining  the  amount  of 
oxygen  required  to  burn  it.  Mix  I  gramme  of  powdered  coal 
and  50  grammes  of  litharge,  or  white  lead  when  pure,  together 
in  a  clay  assay-crucible,  and  cover  with  about  20  grammes  of 
litharge.  Heat  in  a  crucible  furnace,  with  a  gradually  increas- 
ing heat  until  the  fusion  is  complete,  which  will  require  from 
10  to  15  minutes.  Remove  the  crucible  from  the  fire,  pour, 


ANALYSIS   OF  COAL   AND   COKE.  267 

and  when  cold  hammer  and  weigh  the  lead  button.  Pure  car- 
bon should  reduce  34  times  its  own  weight  of  lead  ;  hydrogen, 
102.7  times  its  own  weight. 

One  part  of  pure  carbon  can  raise  the  temperature  of  8080 
parts  of  water  i°;  consequently,  if  the  fuel  is  assumed  as  car- 
bon, its  value  in  heat-units  may  be  estimated  by  multiplying 
8.o.|.o.  by  the  weight  of  the  lead  button  obtained  in  the  assay. 
As  hydrogen  is  always  present  in  the  coal  this  method  neces- 
sarily gives  low  results. 

If  an  elementary  analysis  of  the  coal  has  been  made  to  de- 
termine its  percentage  of  carbon  and  hydrogen,  the  heating 
power  can  be  accurately  determined. 

Elementary  Analysis. — Air  estimation  of  the  total  carbon 
and  hydrogen  which  the  fuel  contains  may  be  made  as  follows : 
The  fuel  is  burned  in  a  stream  of  oxygen,  the  resulting  CO, 
and  H2O  being  caught  in  suitable  apparatus  and  weighed  in 
those  combinations.  The  same  apparatus  as  is  used  for  the 
determination  of  carbonic  acid  and  water  in  white-lead  (see 
Part  II,  Chap.  V,  and  Part  III,  Chap.  XV),  may  be  used  with 
slight  modifications.  Take  a  piece  of  combustion-tubing  about 
28  inches  long,  and  about  one  half  an  inch  internal  diameter, 
fit  to  each  end  corks  through  which  are  passed  tubes  of  about 
one-tenth  inch  internal  diameter  and  4  inches  in  length. 
About  2  inches  from  the  front  end  of  the  tube  (the  end  to 
be  attached  to  the  apparatus  for  absorbing  CO2  and  H2O) 
place  a  plug  of  asbestos  which  has  been  previously  ignited  to 
remove  all  moisture  and  carbonaceous  material.  Back  of 
this  plug  place  enough  freshly-ignited  CuO  to  fill  the  tube  a 
little  more  than  half,  and  push  down  upon  this  another  plug 
of  ignited  asbestos.  Have  at  the  rear  end  of  the  combustion- 
tube  two  bottles,  with  corks  and  tubes,  for  drying  the  oxy- 
gen and  removing  from  it  any  traces  of  CO3  it  may  contain,  by 
bubbling  it  through  the  bottles  containing,  respectively,  con- 
centrated HUSO4  and  strong  KOH,  having  the  H2SO4  bottle 
next  to  the  tube.  For  the  front  end  have  a  tube  filled  with 
neutral  calcium  chloride  in  fragments,  through  which  a  current 
of  dry  CO2  has  passed  for  some  time,  followed  by  a  current  of 


268  A    MANUAL    OF  PRACTICAL   ASSAYING. 

dry  air.  To  this  attach  a  U-tube  filled  with  fresh  soda-lime 
for  the  absorption  of  the  carbonic  acid.  The  coal,  from  which 
the  moisture  has  been  driven  off  by  previous  drying,  is 
weighed  out  into  a  platinum  boat.  Weigh  the  calcium 
chloride  and  the  soda-lime  tubes.  Connect  the  combustion- 
tube  at  the  rear  end  with  the  sulphuric-acid  and  potassium- 
hydrate  bottles,  and  at  the  front  end  with  the  aspirator,  heat 
it  to  redness,  and  then  draw  a  current  of  air  through  it  until 
cool.  Now  introduce  the  platinum  boat  into  the  rear  end  of 
the  tube,  replace  the  cork  and  connect  the  calcium-chloride 
and  soda-lime  tubes  at  the  front  end,  connecting  the  last  with 
the  aspirator.  Draw  a  slow  current  of  air  through  the  tube, 
and  heat  the  front  end  of  the*CuO,  carrying  the  heat  gradually 
forward.  Arrange  it  so  that  the  CuO  shall  be  highly  heated 
before  the  coal  begins  to  burn.  Just  before  the  heat  reaches 
the  boat  attach  the  tube  from  the  oxygen  cylinder,  and  force 
a  slow  current  of  gas  through  the  tube.  Heat  the  coal 
moderately  so  that  it  will  burn  slowly  and  not  give  off  the 
gases  too  rapidly.  When  the  coal  is  completely  consumed, 
disconnect  the  oxygen  cylinder,  remove  the  heat,  and  draw  a 
current  of  dry  air  free  from  carbonic  acid  through  the  appa- 
ratus until  cool.  Detach  the  tubes  and  weigh.  The  increase 
in  the  weight  of  the  calcium-chloride  tube  represents  water  to 
be  calculated  to  H,  and  the  increase  in  weight  of  the  soda-lime 
tube  represents  carbon  dioxide  to  be  calculated  to  C. 


CHAPTER  XL 

ANALYSIS  OF  GASES. 

IN  a  gas  or  metallurgical  works  where  a  number  of  analyses 
of  mixtures  of  gases  are  required  daily  it  is  only  possible  to  do 
the  work  with  simple  apparatus. 

The  following  apparatus  for  the  rapid  analysis  of  gases  and 
the  method  of  using  it  were  first  described  by  A.  H.  Elliott  in 
the  School  of  Mines  Quarterly  (Vol.  Ill,  No.  I,  page  15): 
Whilst  this  method  does  not  compare  with  the  elaborate 
methods  of  Bunsen  and  others,  where  very  delicate  readings 
and  nice  precautions  are  taken,  it  gives  very  good  results  for 
technical  work  and  answers  every  purpose  in  the  everyday 
practice  of  a  gas  or  metallurgical  works. 

The  great  advantages  of  this  method  are  the  rapidity  with 
which  an  analysis  can  be  made  (about  forty-five  minutes)  and 
the  simplicity  and  inexpensiveness  of  the  necessary  apparatus. 

The  apparatus  is  shown  in  the  drawing.  The  tube  A  is  of 
about  125  cc.  capacity,  whilst  B,  although  of  the  same  length, 
holds  only  zoo  cc.  from  the  mark  D,  or  zero,  to  the  mark  on 
the  capillary  tube  at  C,  and  is  carefully  graduated  into  -fa  cc. 
The  attachments  to  these  tubes  below  are  seen  from  the  draw- 
ing, except  that  the  stop-cock  /  is  three-way,  with  a  delivery 
through  its  stem.  The  bottles  K  and  L  hold  about  one  pint 
each.  The  tubes  A  and  B  are  connected  with  each  other  and 
with  the  funnel  M  by  capillary  tubing  about  one  millimetre  in 
internal  diameter.  There  is  a  stop-cock  at  G  and  another  at 
F,  whilst  the  funnel  M,  holding  about  60  cc.,  is  ground  to  fit 
over  the  end  of  F  above.  At  E  a  piece  of  rubber  tubing 
unites  the  ends  of  the  capillary  tubes,  which  are  ground  off 
square  to  make  them  fit  as  closely  as  possible. 

269 


A    MANUAL    OF  PRACTICAL  ASSAYING. 


In  beginning  the  analysis  of  a  mixture  of  gases,  the  stem 
exit  of  the  cock  /  is  closed  by  turning  it  so  that  L  and  A  are 
connected  through  the  rubber  tubing  ;  the  stop-cocks  .Fand  G 
are  opened  and  water  is  allowed  to  fill  the  apparatus  from  the 
bottles  K  and  L,  which  have  been  previously  supplied.  When 
the  water  rises  in  the  funnel  M,  and  all  air-bubbles  have  beea 


forced  out  of  the  tubes,  the  stop-cocks  F  and  G  are  closed,  the 
funnel  M  is  removed,  and  the  tube  delivering  the  gas  to  be 
tested  is  attached  in  its  place.  By  now  lowering  the  bottle  L 
slowly,  and  simultaneously  opening  the  stop-cock  F,  the  tube 
A  is  nearly  filled  with  gas,  and  the  stop-cock  F  is  closed.  The 
tube  delivering  the  gas  is  now  removed,  the  funnel  M  replaced, 
the  bottle  L  raised,  the  bottle  K  lowered,  and  by  opening  the 
stop-cock  G  the  gas  is  transferred  to  the  graduated  tube  B. 
By  placing  the  bottle  L  on  a  stand  at  about  the  level  of  the 
water  in  A,  the  level  in  B  and  in  the  bottle  K  can  be  adjusted 
to  the  zero  point,  and  the  stop-cock  G  is  closed.  The  excess 
of  gas  in  A  is  expelled  by  opening  the  stop-cock  F  and  raising 


ANALYSIS  OF  GASES.  2?  I 

the  bottle  L.  The  gas  remaining  in  the  capillary  tube  between 
C  and  the  vertical  part  is  disregarded,  or  in  very  careful  work 
it  may  be  measured  and  an  allowance  made  in  not  rilling  the 
tube  B  quite  to  the  zero  mark,  but  usually  it  is  too  small  to  be 
worth  notice. 

Having  measured  the  gas  to  be  tested,  it  is  now  transferred 
by  means  of  the  bottles  AT  and  L  into  the  tube  A,  and  the  fluid 
chemicals  added  by  placing  them  in  the  funnel  M  and  allowing 
them  to  flow  down  the  sides  of  the  tube  slowly,  being  careful 
never  to  allow  the  fluids  to  run  below  the  level  of  the  top  of 
the  vertical  tube  in  the  funnel.  It  is  best  to  have  a  mark  on 
the  outside  of  the  funnel  about  three  quarters  of  an  inch  above 
the  top  of  the  level  of  the  vertical  tube,  and  never  to  draw  the 
fluid  down  below  this  point. 

Having  treated  the  gas  with  the  chemical,  it  is  transferred 
by  means  of  the  bottles  to  the  tube  B,  to  be  measured. 
Should  the  chemical  get  into  the  horizontal  capillary  tube,  the 
passage  of  a  little  water  from  the  bottle  K  will  remove  it,  be- 
fore transferring  the  gas.  When  the  gas  residue  is  in  B,  arid  the 
fluid  in  A  has  been  adjusted  at  the  mark  C  on  the  horizontal 
tube,  the  stop-cock  G  is  closed,  the  bottle  K  is  lowered  till  the 
level  of  the  water  in  it  and  that  in  the  tube  B  are  the  same, 
and  the  reading  is  made.  The  tube  A  is  now  filled  with  the 
chemical  just  used  and  water.  By  'turning  the  stem  of  the 
three-way  cock  /,  so  that  it  communicates  with  A,  and  also 
opening  the  stop-cock  F,  the  contents  of  the  tube  can  be  run 
out,  and  water  run  through  the  funnel  M  to  clean  the  tube  for 
a  new  absorption.  When  the  tube  is  clean,  by  turning  the 
stop-cock  /,  so  that  A  and  L  communicate,  the  water  is  forced 
into  A,  and  the  apparatus  is  ready  to  receive  the  gas  for  new 
treatment. 

By  this  means  the  gas  is  removed  from  the  action  of  the 
water  used  to  wash  out  the  chemicals,  and  the  chemicals  are 
completely  removed  from  any  interference  with  each  other 
when  treating  a  mixture  of  gases. 

In  using  this  apparatus  the  solutions  are  added  in  the  fol- 
lowing order  : 


UNIVERSITY 


2/2  A   MANUAL    OF  PRACTICAL   ASSAYING. 

1.  Potassic  hydrate,  to  absorb  carbon  dioxide  (also  hydro- 
gen sulphide  and  sulphurous  oxide  if  present.     If   these  gases 
are  present  in  large  quantities  special  methods  are  necessary 
for  their  estimation). 

2.  Potassium  pyrogallate,  to  absorb  oxygen. 

3.  Bromine,    to   absorb   illuminants,    like  olefiant  gas   and 
acetylene,    and   after    the    absorption    is   complete,    and    the 
bromine  vapors  cause  an  expansion,  a  little  potassium  hydrate 
is  added,  to  absorb  these  vapors  before  the  gas  is  transferred 
and  measured. 

4.  Cuprous  chloride  in  concentrated  hydrochloric-acid  solu- 
tion, to  absorb  carbonic  oxide.     After  this  absorption  is  com- 
plete, the  gas  is  transferred  to  the  measuring  tube,  the  con* 
tents  of  the  tube  A  run  out,  the  tube  washed  and  filled  with 
water  from  the  bottle  L.     The  gas  is  now  transferred  to  A, 
and  treated  with  potassium-hydrate  solution,  to  absorb  hydro- 
chloric-acid vapors,  before  the  final  reading  is  made  in  B. 

The  treatment  up  to  this  point  takes  from  twenty  to  thirty 
minutes,  according  to  the  amount  of  practice  the  operator  has 
had  with  the  apparatus.  The  gas  residue  still  contains  marsh- 
gas,  hydrogen,  and  nitrogen.  By  removing  the  funnel  M  and 
attaching  in  its  place  a  rubber  tube  communicating  with  an 
explosion  eudiometer  in  a  deep  cylinder  of  water  (both  rubber 
tube  and  eudiometer  being  drawn  full  of  water),  a  portion  of 
the  gas  residue  can  be  mixed  with  oxygen,  exploded,  and  the 
contraction  and  the  carbonic  acid  determined ;  the  marsh-gas 
and  hydrogen  being  calculated  by  the  usual  formula.  The 
nitrogen  is  found  by  the  difference  of  the  addition  of  the  other 
constituents  and  one  hundred.  The  explosion-tube  is  a  similar 
tube  to  A,  without  the  lower  attachment  and  the  lateral  capil- 
lary tube  above  ;  the  funnel  M  being  retained,  and  two  plati- 
num wires  being  fused  into  the  glass  near  the  top,  to  give  the 
spark  for  ignition.  It  is  only  necessary  to  clamp  this  tube 
down  upon  a  piece  of  cork  in  a  vessel  of  water  during  explo- 
sion, and  adjust  the  water-level  in  a  tall  cylinder  of  water  when 
making  the  readings  of  contraction  and  absorption  of  carbon 
dioxide. 


ANALYSIS   OF   GASES.  2/3 

The  water  used  in  the  apparatus  should  be  of  the  same 
temperature  as  the  room  in  which  the  analysis  is  made,  and 
by  careful  handling  little  or  none  of  the  chemicals  used  will  get 
into  the  bottle  L. 

When  working  in  a  warm  place  the  tube  B  should  be  sur- 
rounded with  a  water-jacket,  to  prevent  change  of  volume  in 
the  gas  while  under  treatment. 


CHAPTER  XII. 
ANALYSIS   OF   WATER. 

THE  following  easy  method  of  analysis  will  serve  for  the 
determination  of  the  value  of  a  water  for  domestic  or  manu- 
facturing purposes  : 

Determination  of  Total  Solids. — Evaporate  500  cc.  of 
the  water  to  dryness  in  a  weighed  platinum  dish.  The  evapo- 
ration is  made  either  on  the  water-bath,  or  the  dish  may  be 
placed  upon  a  piece  of  asbestos  board  and  evaporated  over  the 
flame  of  a  Bunsen  burner,  care  being  exercised  to  not  allow 
the  contents  of  the  dish  to  boil,  as  this  is  liable  to  result  in 
loss.  Now  heat  the  dish  and  its  contents  in  an  air-bath  at  a 
temperature  of  1 10°  C.  to  constant  weight.  This  weight  will 
represent  the  mineral  constituents  of  the  water  and  the  organic 
and  volatile  matter.  This  weight  in  milligrammes  multiplied 
by  0.2  will  give  the  parts  in  100,000,  and  by  0.1166  the  grains 
per  U.  S.  gallon  of  231  cubic  inches. 

Organic  and  Volatile  Matter. — After  evaporating  and 
weighing  as  above,  heat  the  dish  and  its  contents  at  a  low-red 
heat  until  all  organic  matter  is  consumed  and  the  contents  are 
•white  or  nearly  so.  Now  add  about  50  cc.  of  water  saturated 
with  carbon  dioxide  and  evaporate  on  a  water-bath,  repeat  the 
treatment  with  carbon  dioxide,  and  evaporate  again.  Dry  in 
an  air-bath  at  110°  C.  as  before,  cool,  and  weigh.  The  loss  in 
weight  approximately  expresses  the  amount  of  volatile  and 
organic  matter  in  the  quantity  of  water  taken. 

Analysis  of  Residue. — The  residue  obtained  as  above  is 
now  moistened  with  a  few  drops  of  hydrochloric  acid,  about 
50  cc.  of  hot  water  is  added,  and  the  contents  of  the  dish  again 

274 


ANALYSIS   OF    WATER.  2?$ 

•evaporated  to  dryness,  and  finally  heated  in  an  air-bath  at 
110°  C.  until  there  is  no  longer  any  odor  of  chlorine.  It  is 
now  dissolved  in  hot  water,  a  few  drops  of  hydrochloric  acid 
added,  transferred  to  a  small  beaker,  and  boiled  for  a  few  min- 
utes. It  is  now  filtered  through  a  small  filter,  washed  with  hot 
water,  and  the  insoluble  residue  dried,  ignited,  and  weighed. 
This  weight  expresses  the  amount  of  silica  in  the  quantity  of 
water  taken,  the  results  being*  calculated  as  above. 

The  filtrate  from  the  silica  is  now  boiled  for  a  few  minutes, 
with  the  addition  of  a  few  drops  of  nitric  acid,  to  insure  the 
oxidation  of  any  ferrous  salt  which  may  be  present,  and  made 
decidedly  alkaline  with  ammonia.  It  is  now  boiled  to  expel 
the  excess  of  ammonia,  and  the  precipitated  hydrates  of  iron 
and  alumina  are  filtered  off  through  a  small  filter  and  washed 
until  the  washings  show  no  reaction  for  chlorine  when  tested 
with  a  solution  of  silver  nitrate  and  nitric  acid.  The  precipi- 
tate is  ignited  in  a  platinum  crucible  and  weighed  as  Fe.,O3 
and  A12O3. 

The  filtrate  from  the  iron  and  alumina  is  now  rendered 
decidedly  alkaline  with  an  excess  of  ammonia,  and  an  excess 
of  a  solution  of  ammonium  oxalate  added.  The  solution  is 
boiled  for  a  few  minutes  and  then  allowed  to  cool  ;  when  cold 
it  is  filtered  through  a  small  filter,  and  the  precipitated  calcium 
oxalate  is  washed  thoroughly  with  hot  water.  In  case  the 
water  contains  much  magnesia  it  will  be  necessary  feo  dissolve 
this  precipitate  in  a  little  hydrochloric  acid  and  water,  and 
reprecipitate  with  ammonia  and  ammonium  oxalate.  (See 
Part  II,  Chap.  XXIII  and  Chap.  XXIV.)  The  calcium  oxa- 
late is  then  ignited  over  a  Bunsen  burner,  and  finally  over  a 
blast-lamp  to  constant  weight,  and  weighed  as  CaO.  The 
results  are  calculated  by  the  use  of  the  same  factors  as  above. 

The  filtrate  from  the  lime  is  evaporated  to  about  75  cc., 
cooled,  and  5  cc.  of  hydrodisodic-phosphate  solution  added.  It 
is  stirred  with  a  glass  rod  for  a  few  minutes,  avoiding  allowing 
the  rod  to  touch  the  sides  of  the  beaker,  and  allowed  to  stand 
several  hours  in  a  cold  place.  It  is  filtered  onto  a  small  filter 
.and  washed,  until  free  from  chlorine,  with  a  solution  of  ammo- 


2/6  A    MANUAL    OF  PRACTICAL   ASSAYING. 

nium  nitrate  (i  gm.  salt  in  10  cc.  of  water).  It  is  dried, 
ignited,  and  weighed  as  Mg3PaO,.  The  weight  of  the  precipi- 
tate in  milligrammes  multiplied  by  0.07206  will  give  the  parts- 
by  weight  of  MgO  in  100,000  parts  of  water,  and  multiplied 
by  0.042  will  give  the  number  of  grains  of  MgO  in  one  U.  S. 
gallon. 

In  the  case  of  a  very  pure  water,  it  will  be  necessary  to 
take  a  greater  quantity  of  the  water  than  500  cc.,  but  in  most 
cases  a  half  litre  will  be  sufficient. 

Determination  of  Alkalies. — From  i  to  5  litres  of  water 
are  evaporated  in  a  platinum  dish  to  about  100  cc.  The  solu- 
tion is  acidified  slightly  with  hydrochloric  acid  ;  a  saturated 
solution  of  barium  hydrate  is  added  until  the  solution  is- 
strongly  alkaline ;  the  solution  is  boiled,  the  precipitate  filtered 
off  and  thoroughly  washed  with  hot  water  until  the  washings 
are  free  from  chlorine.  To  the  filtrate  ammonium  carbonate 
is  added  as  long  as  a  precipitate  is  produced,  the  solution  is 
boiled,  and  the  precipitated  barium  carbonate  filtered  off  and 
washed  with  hot  water  until  the  washings  no  longer  give  a 
reaction  for  chlorine.  The  filtrate  is  evaporated  to  dryness, 
and  heated  at  a  low-red  heat,  to  burn  out  the  ammonium 
chloride.  Take  the  dry  mass  up  with  hot  water  and  repeat 
the  treatment  with  barium  hydrate  and  ammonium  carbonate, 
to  insure  the  complete  removal  of  the  magnesia  which  may 
have  been  held  in  solution  by  the  alkaline  chlorides.  Finally, 
evaporate  the  filtrate  to  dryness  in  a  weighed  platinum  dish, 
expel  all  ammonium  chloride  present  by  heating  to  a  low-red 
heat,  cool,  and  weigh  the  mixed  chlorides  of  potassium  and 
sodium.  The  potassium  and  sodium  may  be  separated  and 
determined  as  described  in  Part  II,  Chapter  XXVI. 

The  weight  of  potassium  platinic  chloride  obtained  (in 
grammes),  multiplied  by  0.30557,  will  give  the  weight  of  the 
potassium  chloride,  which  weight  subtracted  from  the  weight 
of  the  mixed  chlorides  previously  obtained  will  give  the  weight 
of  the  sodium  chloride.  The  weight  (in  milligrammes)  of  the 
sodium  chloride  obtained  from  the  treatment  of  500  cc.  of 
water,  multiplied  by  0.0788  and  0.1061,  will  give  the  parts  of 


ANALYSIS   OF    WATER.  2/7 

Na  and  Na3O,  respectively,  in  100,000  parts  of  water.  For  the 
same  conversion  of  potassium  chloride  the  factors  are  0.1049 
and  0.1263.  To  convert  parts  in  100,000  into  grains  per  U.  S. 
gallon,  multiply  by  0.583. 

Determination  of  Sulphuric  Acid. — Acidify  500  cc.  of 
water  with  about  5  cc.  of  hydrochloric  acid,  and  evaporate  to 
about  150  cc.  Filter,  if  necessary;  boil  the  solution,  and 
whilst  boiling  add  an  excess  of  a  hot  solution  of  barium  chlo- 
ride. Boil  for  a  few  minutes  and  allow  to  cool.  Filter,  wash 
with  hot  water,  dry,  ignite,  and  weigh  the  BaSO4.  The  weight 
of  this  precipitate  in  milligrammes  multiplied  by  0.0687  gives 
the  number  of  parts  of  SO,  in  100,000  parts  of  water,  and 
multiplied  by  0.04  the  number  of  grains  of  SO3  in  one  U.  S. 
gallon. 

Determination  of  Chlorine. — The  determination  of  chlo- 
rine is  best  made  volumetrically  as  follows :  Prepare  a  standard 
solution  of  silver  nitrate  by  dissolving  4.788  gms.  of  c.  p.  crys- 
tallized nitrate  of  silver  in  distilled  water  and  diluting  to  1000 
cc.  Each  cubic  centimetre  of  this  solution  should  precipitate 
exactly  I  mg.  of  chlorine.  This  solution  may  be  standard- 
ized by  means  of  a  dilute  solution  of  pure  fused  sodium  chlo- 
ride. A  solution  of  potassium  chromate,  made  by  dissolving 
5  gms.  of  the  pure  salt  in  about  100  cc.  of  water,  is  used  as  an 
indicator. 

To  determine  the  chlorine,  transfer  100  cc.  of  the  water  to 
be  examined  to  a  porcelain  evaporating  dish,  add  2  cc.  of  the 
indicator  solution,  and  then  run  in  from  the  burette  the  stand- 
ard solution  of  silver  nitrate  until  the  red  precipitate  of  chro- 
mate of  silver,  which  is  at  first  decomposed  by  the  excess  of 
chlorine,  is  just  permanent.  The  burette  reading  will  give 
directly  the  number  of  parts  of  chlorine  to  100,000  parts  of 
water.  To  convert  this  into  parts  in  one  U.  S.  gallon  multiply 
by  0.583. 

For  domestic  purposes  the  amount  of  organic  matter,  free 
and  albuminoid  ammonia  which  the  water  contains  is  very 
important. 

Permanganate  Test. — This  test  is  made  to  determine  the 


278  A    MANUAL   OF  PRACTICAL  ASSAYING. 

amount  of  oxidizable  organic  matter  in  water,  and  is  claimed 
by  some  chemists  to  be  quite  as  valuable  as  the  determination 
of  the  albuminoid  ammonia.  The  test  requires  a  solution  of 
oxalic  acid  and  a  solution  of  potassium  permanganate,  which 
are  prepared  as  follows:  Dissolve  0.7875  gm.  of  pure  crystal- 
lized oxalic  acid  in  looo  cc.  of  water.  One  cc.  of  this  solution 
will  be  equivalent  to  one  tenth  of  a  milligramme  of  oxygen,  as 
0.7875  mgm.  of  oxalic  acid  requires  o.i  mgm.  of  oxygen  for  con- 
version to  carbonic  acid.  Dissolve  0.500  gm.  of  pure  potassium 
permanganate  in  1000  cc.  of  water,  and  dilute  until  I  cc.  of  the 
solution  exactly  oxidizes  I  cc.  of  the  oxalic-acid  solution.  Then 
I  cc.  of  the  potassium-permanganate  solution  carries  one  tenth 
of  a  milligramme  of  available  oxygen. 

To  .200  cc.  of  the  water  add  3  cc.  of  dilute  sulphuric  acid, 
and  then  from  a  burette  the  permanganate  solution  until  the 
color  produced  by  it  ceases  to  disappear  after  allowing  to  stand 
three  hours.  From  the  number  of  cc.  of  permanganate  solu- 
tion used  calculate  the  quantity  of  oxygen  required  to  oxidize 
organic  matter.  It  is  assumed  that  the  oxygen  required  mul- 
tiplied by  8  is  equivalent  to  organic  matter. 

Free  and  Albuminoid  Ammonia. — The  determination  of 
these  requires  the  following  solutions: 

Nesslers  Solution. — Dissolve  50  gms.  of  potassium  iodide  in 
a  small  quantity  of  hot  water,  place  the  solution  on  a  boiling- 
water  bath;  cool,  add,  with  frequent  agitation,  a  strong  solution 
of  mercuric  chloride  (40  gms.  of  the  salt  and  300  cc.  of  water), 
until  the  red  precipitate  just  redissolves;  filter;  add  to  the 
filtrate  a  strong  solution  of  potassium  hydrate  containing  200 
gms.  of  the  salt;  filter;  dilute  to  1000  cc.,  add  5  cc.  of  a  satu- 
rated solution  of  mercuric  chloride,  allow  the  precipitate  formed 
to  settle,  decant  the  clear  liquid,  and  keep  for  use  in  a  tightly 
stoppered  bottle. 

Sodium-carbonate  Solution. — Add  100  gms.  of  sodium  car- 
bonate to  200  cc.  of  distilled  water  free  from  ammonia,  and 
keep  in  a  well-corked  bottle. 

Potassium-permanganate  Solution. — Dissolve  200  gms.  of 
potassium  hydrate  and  8  gms.  of  potassium  permanganate  in 


ANALYSIS   OF    IVATER.  279 

1000  cc.  of  distilled  water  free  from  ammonia,  boil  hard  for 
half  an  hour  in  a  two-litre  flask  to  expel  ammonia,  and  keep  in 
a  well-corked  bottle. 

Ammonium  Solution. — Dissolve  0.3883  gm.  of  ammonium 
sulphate  or  0.315  gm.  of  ammonium  chloride  in  1000  cc.  of 
pure  distilled  water  free  from  ammonia.  One  cc.  of  either 
-solution  will  contain  one  tenth  of  a  milligramme  of  ammonia 
{NH3).  For  use  dilute  to  ten  volumes,  so  that  each  cc.  will 
contain  one  hundredth  of  a  milligramme  of  ammonia. 

Distilled  Water  free  from  Ammonia. — To  ordinary  distilled 
water  add  a  little  sodium  carbonate,  and  boil,  in  a  large  flask, 
-until  about  one  fourth  is  evaporated,  then  distil  the  remainder 
from  a  retort  holding  about  1500  cc.  until  the  distillate  gives 
no  reaction  for  ammonia  with  Nessler's  solution,  testing  50  cc. 
of  the  distillate  at  a  time.  When  no  more  ammonia  can  be 
•detected,  distil  off  into  a  large  flask  750  cc.,  and  test  again  to 
be  sure  the  750  cc.  are  free  from  ammonia.  Proceed  in  this 
manner  until  sufficient  is  prepared,  and  keep  the  water  in 
tightly  stoppered  bottles. 

Free  Ammonia. — To  determine  the  free  ammonia  in  a  water 
connect  a  glass  retort  of  at  least  1000  cc.  capacity  with  a 
condenser,  and  cleanse  the  apparatus  by  distilling  some  clean 
water.  Introduce  200  cc.  of  clean  water  and  15  cc.  of  the 
sodium-carbonate  solution,  and  distil  until  the  distillate  is  free 
from  ammonia.  Now  introduce  500  cc.  of  the  water  to  be 
tested,  and  distil,  collecting  the  distillate  in  test  cylinders.  In 
other  cylinders  of  the  same  calibre  add  amounts  of  the  stand- 
ard ammonia  solution  containing,  respectively,  o.oi,  0.02,  etc., 
mgm.  NH3,  and  dilute  each  up  to  50  cc.  with  the  especially 
prepared  distilled  water.  When  50  cc.  have  distilled  over, 
add  1.5  cc.  of  the  Nessler  solution  to  each  cylinder.  Care 
should  be  exercised  to  always  use  the  same  Nessler  solution, 
the  same  amounts,  and  to  allow  it  to  act  as  nearly  as  possible 
for  the  same  length  of  time.  After  allowing  the  cylinders  to 
stand  a  few  minutes  compare  the  tint  of  the  distillate  with  those 
of  the  comparison  cylinders,  and  thus  estimate  the  amount  of 
ammonia  present.  Test  each  succeeding  50  cc.  in  the  same 


280  A    MANUAL    OF  PRACTICAL  ASSAYING. 

way,  and  proceed  until  the  last  50  cc.  tested  contains  less  than 
o.oi  gm.  of  NH8.  The  whole  amount  of  ammonia  thus  deter- 
mined is  the  total  free  ammonia.  Should  the  water  contain 
much  ammonia  it  is  safer  to  thoroughly  mix  each  50  cc.  of  the 
distillate  and  take  out  10  cc.,  dilute  it  to  50  cc.,  and  test  as 
above.  The  remaining  four  fifths  of  the  distillate  may  be  used 
to  confirm  the  results  thus  obtained. 

Albuminoid  Ammonia. — After  having  determined  the  free 
ammonia  as  above,  add  50  cc.  of  the  permanganate  solution  ta 
the  contents  of  the  retort  and  distil  until  the  distillate  no  longer 
shows  the  presence  of  ammonia.  Now  add  500  cc.  of  the  water 
to  be  tested,  and  distil,  testing  each  50  cc.  of  the  distillate,, as 
before,  until  it  contains  less  than  o.oi  mg.  of  NH3.  This  gives 
the  total  ammonia.  The  difference  between  the  total  and  the 
free  gives  the  albuminoid  ammonia. 

Nitrates. — The  following  method  is  quite  simple,  and  ap- 
parently more  accurate  than  the  usual  method.*  Rinse  a  lOO-cc. 
Nessler  tube  with  the  water  to  be  tested,  and  then  fill  to  the 
loocc.  mark  with  the  water  to  be  tested.  Drop  in  5  to  10  gms. 
of  freshly-prepared  sodium  amalgam,  the  amount  varying  with 
that  of  the  nitrates  presumably  present.  Enough  should  be 
added  to  keep  up  the  action  at  ordinary  temperatures  for  at 
least  two  hours.  Cover  with  a  watch-glass,  and  allow  the  tube 
to  stand  in  an  atmosphere  free  from  ammonia  vapors,  after 
adding  one  or  two  drops  of  concentrated  hydrochloric  acid  (free 
from  ammonium  salt).  After  two  hours  the  solution  should 
only  be  faintly  acid  ;  if  decidedly  acid,  add  more  sodium  amal- 
gam, and  continue  the  reduction.  Finally,  filter  through  a 
small  filter  previously  freed  from  all  traces  of  ammonia  and 
Nesslerize  50  cc.  of  the  filtrate  in  the  usual  manner.  Deduct 
the  free  ammonia  which  the  water  contains,  as  determined  in 
a  separate  portion,  and  calculate  the  results  as  usual. 

*  School  of  Mines  Quarterly,  Vol.  XV,  No.  i,  p.  u. 


ANALYSIS   OF    WATER.  28 1 

Grouping  of  the  Constituents. — It  is  impossible  to  give 
any  exact  rule  for  the  proper  grouping  of  the  constituents,  as 
determined  by  the  analysis.  The  following  will  answer  for 
ordinary  water:  Combine  the  sodium  with  chlorine  as  sodium 
chloride.  Should  there  be  more  sodium  than  the  chlorine  will 
satisfy,  combine  the  excess  with  sulphuric  acid  as  sodium  sul- 
phate. Should  there  not  be  sufficient  sulphuric  acid  to  satisfy 
all  the  sodium,  combine  the  excess  with  carbonic  acid  as 
sodium  carbonate.  Combine  the  potassium  with  sulphuric  acid 
as  potassium  sulphate.  Should  there  be  more  sulphuric  acid 
than  the  potassium  and  the  excess  of  sodium  (over  NaCl)  will 
satisfy,  combine  the  excess  first  with  calcium  as  calcium  sul- 
phate, and  any  further  excess  with  magnesium  as  magnesium 
sulphate.  Should  the  water  contain  a  large  amount  of  chlorine 
(in  excess  of  the  amount  sufficient  to  satisfy  the  sodium),  and 
not  sufficient  sulphuric  acid  to  satisfy  the  potassium,  combine 
the  excess  of  potassium  with  chlorine,  and  should  there  be  any 
chlorine  still  left,  combine  it  first  with  magnesium,  and  if  there 
is  still  an  excess,  combine  it  with  calcium.  Calculate  all  cal- 
cium and  magnesium  not  combined  with  chlorine  and  sulphuric 
acid  to  carbonates. 


CHAPTER   XIII. 
ACIDIMETRY  AND  ALKALIMETRY. 

AciDIMETRY  and  alkalimetry  is  the  determination  of  the 
amount  of  acid  or  alkali  which  a  solution  contains.  It  is  ac- 
complished by  means  of  standard  alkali  and  standard  acid  so- 
lutions and  suitable  indicators. 

Standard  Acid  Solutions. — The  usual  solutions  employed 
are  solutions  of  sulphuric,  hydrochloric,  and  nitric  acids  in 
water.  In  addition  to  these,  other  acid  solutions,  as  oxalic 
and  acetic,  are  occasionally  employed.  The  choice  of  the  acid 
will  depend  largely  upon  the  character  of  the  substance  to 
be  analyzed,  certain  acids  being  particularly  adapted  to  cer- 
tain determinations. 

Half-normal  SulpJiuric  Acid. — This  solution  is  prepared  so- 
that  it  will  contain  exactly  0.04  gm.  of  SO3  or  0.049  gm<  °f 
HaSO4  in  each  cc.  To  prepare  the  solution  add  33.3  cc.  of  c.  p. 
concentrated  sulphuric  acid  to  1000  cc.  of  water,  mix  thor- 
oughly, and  allow  to  cool  to  the  normal  temperature  of  the 
laboratory.  Partially  fill  a  burette  with  the  solution,  and  draw 
off  into  beakers  two  separate  portions  of  exactly  15  cc.  each. 
To  each  portion  add  about  50  cc.  of  water  and  30  cc.  of  a 
saturated  solution  of  barium  chloride,  having  both  the  acid 
solution  and  the  barium-chloride  solution  at  the  boiling-point 
when  the  addition  is  made.  Filter  off  the  precipitates  of  barium 
sulphate,  and  determine  the  sulphuric  acid  as  usual.  If  the 
precipitates  do  not  differ  in  weight  more  than  o.oi  gm.,  take 
the  average  and  calculate  the  sulphuric  acid  in  I  cc.  of  the 
solution.  Suppose  the  calculation  shows  that  ice.  of  the  solu- 
tion contains  0.042  gm.  of  SO3  in  place  of  0.04  gm.,  then  it  is 

282 


ACIDIMETRY  AND  ALKALIMETRY.  283 

too  strong  and  requires  dilution.  As  I  cc.  contains  0.042  gm., 
1000  cc.  will  contain  42  gms.  in  place  of  4Ogms.,  which  it  should 
contain ;  consequently, 

40  gms.  :  looo  cc.  ::  42  gms.  :  1050  cc. 

Hence  50  cc.  of  water  must  be  added  to  each  1000  cc.  of  the 
acid  solution  to  make  it  half  normal.  To  do  this  fill  a  dry 
looo-cc.  flask  to  the  holding  mark  with  the  solution,  pour  the 
solution  from  the  flask  into  a  clean  dry  bottle,  run  into  the 
flask  50  cc.  of  water,  shake  well,  and  pour  off  into  the  bottle. 
Shake  the  bottle  well  and  pour  back  into  the  flask ;  finally  pour 
back  into  the  bottle,  where  it  is  kept  for  use.  The  sulphuric 
acid  should  be  determined  in  the  solution  again,  and  the  solu- 
tion corrected  as  before. 

Normal  Nitric  Acid. — To  prepare  this  solution  add  100  cc. 
of  c.  p.  nitric  acid  of  1.32  sp.  gr.  to  765  cc.  of  water  and 
thoroughly  mix.  The  best  method  of  determining  the 
strength  of  this  solution  is  by  means  of  a  normal  solution  of 
potassium  or  sodium  hydrate  which  has  previously  been 
accurately  standardized.  One  cc.  of  the  acid  solution  should 
exactly  neutralize  I  cc.  of  the  standard  alkali  solution.  Have 
two  burettes  in  a  stand,  and  fill  one  with  the  acid  solution  to  be 
tested  and  the  other  with  the  standard  alkali  solution.  Draw 
off  10  cc.  of  the  acid  solution,  dilute  with  100  cc.  of  water, 
add  a  few  drops  of  a  suitable  indicator,  as  litmus  solution,  and 
run  in  the  standard  alkali  solution  until  the  color  just  changes 
from  red  to  blue.  Take  the  reading  of  the  burette  and  run  in 
another  10  cc.  of  the  acid  solution,  and  titrate  again  with  the 
standard  alkali  solution.  The  two  readings  of  the  burette 
should  agree  closely.  Suppose  this  trial  shows  that  10  cc.  of 
the  acid  solution  neutralizes  12  cc.  of  the  standard  alkali  solu- 
tion, then  the  acid  solution  is  too  strong  and  requires  dilution. 
In  this  case  every  100  cc.  of  the  acid  solution  should  be  diluted 
to  1 20  cc.  Measure  off  800  cc.  of  the  acid  solution  and  add 
160  cc.  of  water,  thoroughly  mix  as  in  the  case  of  the  sul- 
phuric-acid solution,  and  restandardize,  continuing  the  opera- 
tion until  the  acid  solution  exactly  neutralizes  the  standard 


284  A   MANUAL   OF  PRACTICAL  ASSAYING. 

alkali  solution,  cc.  for  cc.  The  nitric-acid  solution  should  con. 
tain  0.063  gm.  of  nitric  acid  in  each  cc. 

Normal  Hydrochloric  Acid* — The  normal  hydrochloric  acid 
solution  should  contain  0.0365  gm.  of  hydrochloric  acid  in 
each  cc.  To  prepare  this  solution  mix  1000  cc.  of  water  with 
200  cc.  of  c.  p.  hydrochloric  acid  of  1.12  sp.  gr.  The  amount  of 
hydrochloric  acid  in  each  cc.  of  the  thoroughly  mixed  solution 
may  be  determined  in  several  ways.  If  some  standard  alkali 
solution  is  on  hand,  its  standard  may  be  readily  determined  by 
the  same  method  as  described  above  for  nitric  acid.  If  it  is 
desired  to  determine  the  hydrochloric  acid  in  each  cc.  directly, 
the  following  method  is  as  good  as  any  :  Draw  off  two  por- 
tions of  the  acid  solution  of  exactly  10  cc.  each  into  a  flask 
\vith  sloping  sides.  Dilute  with  warm  water,  and  precipitate  the 
chlorine  completely  with  a  strong  solution  of  nitrate  of  silver. 
Shake  the  flask,  fill  it  completely  with  warm  water,  and  invert 
it  over  a  porcelain  crucible  of  suitable  size.  Allow  the  precip- 
itate to  settle  completely  into  the  crucible,  remove  the  flask, 
and  pour  off  the  water  from  the  crucible.  Remove  the  last 
particles  of  water  from  the  crucible  with  a  piece  of  blotting- 
paper,  being  careful  not  to  remove  any  of  the  precipitate. 
Evaporate  off  the  last  traces  of  water,  and  dry  the  crucible  and 
its  contents  in  a  drying-chamber.  When  thoroughly  dry,  heat 
over  a  low  flame  until  the  silver  chloride  begins  to  fuse  around 
the  edges  ;  cool,  and  weigh.  Deduct  from  this  weight  the 
known  weight  of  the  crucible.  The  remainder  will  be  the 
weight  of  the  silver  chloride.  To  obtain  the  weight  of  the 
chlorine  multiply  this  weight  by  $-fr|.  From  this  weight  calcu- 
late the  number  of  cc.  of  water  or  hydrochloric  acid  to  add  to 
a  given  quantity  of  the  acid  solution  in  order  to  make  it  nor- 
mal. Make  the  necessary  addition,  and  restandardize  as  before. 

Half-normal  Oxalic  Acid. — To  prepare  this  solution  dis- 
solve 63  gms.  of  c.  p.  crystallized  oxalic  acid  in  1000  cc.  of 
water,  and  standardize  by  titrating  a  portion  with  standard 
alkali  solution  ;  or  the  oxalic  acid  may  be  determined  by  means 
of  a  standard  solution  of  potassium  permanganate.  (See  Part 
II,  Chap.  XVI,  Iron.) 


ACIDIMETRY  A^D  ALKALIMETRY.  285 

As  the  oxalic-  and  sulphuric-acid  solutions  are  readily  and 
accurately  standardized,  they  are  extremely  useful  in  making- 
up  different  standard  acid  and  alkali  solutions.  Once  having 
obtained  a  perfectly  normal  acid  solution,  the  other  solutions 
.are  readily  obtained  by  standardizing  with  the  normal  or  half- 
normal  acid  solution. 

Standard  Alkali  Solutions. — The  solutions  generally  em- 
ployed are  normal  potassium-hydrate,  normal  sodium-hydrate, 
and  occasionally  half-normal  sodium-carbonate  solutions. 

Normal  Potassium  Hydrate. — This  solution  should  contain 
exactly  0.0561  gm.  of  potassium  hydrate,  or  0.0471  gm.  of 
potassium  oxide  (K2O),  in  each  cc.  To  prepare  the  solution 
dissolve  40  gms.  of  pure  potassium  hydrate  in  600  cc.  of  water, 
and  when  dissolved  mix  thoroughly  and  fill  a  burette  with 
the  solution.  Run  into  a  beaker  .exactly  10  cc.  of  the  stand- 
ard sulphuric  acid  (or  other  standard  acid)  solution,  dilute 
with  water  to  about  200  cc.,  add  a  few  drops  of  the  indicator, 
and  run  in  the  potassium  hydrate  solution,  drop  by  drop 
towards  the  last,  until  the  color  changes.  Note  the  reading  of 
the  burette,  and  add  another  10  cc.  of  the  acid  solution  and 
titrate  again.  Repeat  this  titration  several  times,  and  take 
the  average  of  the  different  determinations,  provided  they 
do  not  differ  too  much.  The  color  imparted  to  any  number 
of  cc.  of  the  acid  solution  by  the  indicator  should  change  upon 
the  addition  of  the  same  number  of  cc.  of  the  alkali  solution. 
If  it  does  not,  the  potassium-hydrate  solution  should  be  diluted 
or  strengthened  until  the  two  agree.  Suppose  it  only  re- 
quired 9  cc.  of  the  potassium-hydrate  solution  to  neutralize 
10  cc.  of  the  half-normal  sulphuric  acid  solution.  Then  every 
9  cc.  of  the  alkali  solution  requires  I  cc.  of  water,  or  500  cc. 
of  the  alkali  solution  require  55.5  cc.  of  water. 

Normal  Sodium  Hydrate. — Every  cc.  of  this  solution  should 
contain  exactly  0.04  gm.  of  sodium  hydrate  or  0.031  gm.  of 
sodium  oxide  (Na2O).  To  prepare  this  solution  dissolve  28 
gms.  of  pure  sodium  hydrate  in  600  cc.  of  water,  mix,  and 
titrate  as  in  the  case  of  the  potassium-hydrate  solution. 

Indicators. — This  is  the  name  given  to  the  coloring  mat- 


286  A   MANUAL   OF  PRACTICAL  ASSAYING. 

ters  used  to  show  when  the  fluid  is  acid  or  alkaline.  A  great 
number  have  been  proposed,  of  which  the  following  are  most 
commonly  used  : 

Litmus. — A  solution  of  litmus  is  prepared  by  boiling  the 
coarsely  powdered  litmus  with  alcohol  of  about  80  per  cent 
two  or  three  times,  and  discarding  the  liquid  so  obtained.  The 
litmus  is  now  digested  repeatedly  with  cold  water  until  all  the 
soluble  coloring  matter  is  extracted.  Allow  the  mixed  wash- 
ings  to  settle,  decant  the  clear  liquid,  and  add  a  few  drops  of 
concentrated  sulphuric  acid  until  the  solution  is  quite  red. 
Heat  to  boiling  to  decompose  the  alkaline  carbonates  and  con- 
vert them  into  sulphates,  arid  then  gradually  add  baryta-water 
until  the  blue  color  is  restored.  Allow  the  precipitated  barium 
sulphate  to  settle  completely,  and  decant  the  solution  into  an 
open  bottle.  The  solution  must  be  kept  in  an  open  bottle,  and 
in  a  place  free  from  acid  or  alkaline  fumes.  It  cannot  be  used 
in  the  presence  of  carbonic  acid. 

Cochineal. — Take  about  3  gms.  of  powdered  cochineal  and 
macerate,  frequently  shaking,  with  a  mixture  of  distilled  water 
and  alcohol  (3  volumes  of  water  and  I  volume  of  alcohol). 
Filter  into  a  stoppered  bottle.  It  should  be  kept  tightly 
corked.  It  cannot  be  used  in  the  presence  of  iron  salts,  but 
is  not  affected  by  carbonic  acid  in  moderate  quantities.  The 
solution  is  yellow  when  acid,  and  carmine  when  alkaline. 

Coralline. — Dissolve  some  coralline  in  alcohol  and  filter 
if  necessary.  Keep  in  a  closed  bottle.  The  solution  becomes 
straw  color  when  acid.  It  is  particularly  well  adapted  to  the 
titration  of  acetic  and  other  organic  acids. 

Methyl  Orange. — This  is  a  very  sensitive  indicator  for 
mineral  acids. 

Phenolphthalein. — This  is  a  very  sensitive  indicator,  and  is 
used  in  the  titration  of  solutions  of  molybdic  acid. 

Logwood. — It  must  be  kept  unexposed  to  the  light,  and  can- 
not be  used  in  the  presence  of  the  oxides  of  the  heavy  metals. 
To  prepare,  boil  a  few  shavings  of  the  logwood  with  distilled 
water  and  mix  the  concentrated  solution  with  I  or  2  volumes 
of  alcohol. 


ACIDIMEl^RY  AND   ALKALIMETRY.  287 

These  standard  solutions  have  a  great  number  of  uses  in 
analytical  chemistry.  A  few  of  their  applications  will  serve  to 
show  the  manner  of  using  them. 

Determination  of  Potassium  Hydrate  in  Commercial  Caustic 
Potash. — In  order  to  save  time  and  possible  errors  in  the  calcu- 
lation of  results  it  is  best  to  weigh  out  an  equivalent  part.  As 
the  molecular  weight  of  caustic  potash  is  56.1,  a  one-tenth 
equivalent  would  be  5.61  gms.  Weigh  out  this  amount,  dis- 
solve in  a  little  hot  water,  filter,  and  thoroughly  wash  the 
residue,  filtering  into  a  loo-cc.  flask.  Bring  the  bulk  of  the 
solution  up  to  exactly  100  cc.,  and  thoroughly  mix  by  pouring 
from  the  flask  into  a  dry  clean  beaker  and  from  the  beaker 
back  into  the  flask,  repeating  several  times.  Fill  a  burette  with 
the  solution  and  draw  off  exactly  10  c.c.  into  a  beaker.  Run 
in  10  cc.  of  the  half-normal  sulphuric  acid,  dilute  to  about  50 
cc.  with  water,  and  add  a  few  drops  of  the  indicator.  Now 
run  in  normal  potassic-hydrate  solution  until  the  solution  is 
exactly  neutral.  Repeat  on  several  other  portions  of  10  cc. 
each,  and  take  the  average.  If  the  caustic  potash  contained 
100  per  cent  of  KOH,  the  10  cc.  of  acid  would  have  just  neu- 
tralized the  10  cc.  of  alkali  solution  taken.  Suppose  2  cc.  of 
the  normal  potassic-hydrate  solution  were  used  :  then  without 
calculation  we  see  at  once  that  the  commercial  alkali  contains 
80  per  cent  potassium  hydrate. 

Analysis  of  Commercial  Acetic  Acid. — Weigh  out,  in  a 
counterpoised  beaker,  30  gms.  of  the  acid,  wash  with  water 
into  a  5OO-CC.  flask,  and  dilute  with  water  to  the  holding  mark. 
Draw  off  with  a  pipette  100  cc.,  run  into  a  beaker,  and  add  a 
few  drops  of  a  suitable  indicator.  Coralline  is  preferable  in  this 
case.  Now  run  in  normal  potassium-hydrate  solution  until  a 
full  alkaline  color  is  obtained.  The  color  should  be  full  alka- 
line, as  neutral  alkaline  acetates  have  a  slight  alkaline  reaction. 
Note  the  reading  of  the  burette  and  calculate  the  per  cent  of 
acid.  If  30  gms.  of  acid  were  taken  and  diluted  to  500  cc.,  of 
which  solution  100  cc.  were  taken  for  titration,  each  cc.  of 
normal  alkali  solution  will  represent  I  per  cent  of  acid. 

If  it  is  desired  to  know  the  weight  of  acid  in  so  many  gal- 


288  A    MANUAL    OF  PRACTICAL  ASSAYING. 

Ions  of  acid,  weighing  of  the  solution  is  unnecessary.  In  this 
case  measure  out  a  portion  of  acid,  dilute,  and  take  an  aliquot 
portion  for  titration. 

As  commercial  acetic  acid  frequently  contains  both  sul- 
phuric and  hydrochloric  acids,  simple  titration  will  not  show 
the  percentage  of  acetic  acid  in  the  case  of  an  impure  acid. 
In  this  case  the  hydrochloric  acid  may  be  determined  volu-  . 
metrically  by  means  of  a  standard  solution  of  silver  nitrate, 
using  potassium  chromate  as  an  indicator.  The  suiphuric  acid 
should  be  determined  by  acidifying  a  weighed  portion  of  the 
acetic  acid  with  hydrochloric  acid,  diluting  with  water,  boiling, 
and  precipitation  with  barium-chloride  solution.  The  weights 
of  hydrochloric  acid  and  sulphuric  acid  so  found  are  then  cal- 
culated to  their  proper  equivalents  in  cc.  of  normal  potassium- 
hydrate  solution,  and  the  corresponding  deduction  from  the 
total  number  of  cc.  of  potassium  hydrate  used  is  made.  The 
difference  will  show  the  per  cent  of  acetic  acid  present.  For 
example,  suppose  3  gms.  of  acetic  acid  were  taken  and  the 
hydrochloric  acid  found  was  0.031  gm.  For  the  determination 
of  sulphuric  acid  3  gms.  were  also  taken,  the  result  being  .025 
gm.  sulphuric  acid.  Now  as  6  gms.  of  acetic  acid  are  taken 
for  titration  in  each  case,  we  have  in  the  6  gms.  0.062  gm.  of 
hydrochloric  and  0.05  gm.  of  sulphuric  acid.  The  hydrochloric 
acid  would  neutralize  1.7  cc.  of  the  normal  alkali  solution  and 
the  sulphuric  acid  would  neutralize  I  cc.  of  the  normal  alkali 
solution ;  hence  from  the  total  number  of  cc.  of  the  normal 
alkali  solution  used  in  the  titration  a  deduction  of  2.7  cc. 
should  be  made  for  the  hydrochloric  and  sulphuric  acids 
present. 


CHAPTER  XIV. 
CHLORIMETRY. 

CHLORIMETRY  has  for  its  object  the  determination  of  the 
available  chlorine  of  bleaching-powder. 

Bleaching-powder,  which  is  commercially  known  as  chloride 
of  lime,  consists  of  a  mixture,  or  combination,  of  calcium  hypo- 
chlorite  (CaQ2O2)  and  calcium  chloride  (CaCla).  Its  value  for 
commercial  and  metallurgical  purposes  will  depend  upon  the 
amount  of  chlorine  set  free  (available  chlorine)  when  an  acid 
is  added.  The  reaction  which  takes  place  is  as  follows : 

Ca(ClO)2 ,  CaCl2  +  2H2SO4  =  2CaSO4  +  2H2O  +  40. 

Hence  the  available  chlorine  is  two  atoms  of  Cl  for  each  atom 
of  O  in  the  hypochlorite. 

A  number  of  methods  have  been  proposed  for  the  estima- 
tion of  the  chlorine  set  free.  The  following  is  believed  to  be 
as  simple  and  accurate  as  any : 

Weigh  out  10  gms.  of  the  bleaching-powder,  transfer  to  a 
porcelain  mortar,  add  about  50  cc.  of  water,  and  rub  into  a 
cream.  Allow  the  coarse  particles  to  settle,  pour  off  the  turbid 
fluid  into  a  looo-cc.  flask,  add  more  water,  rub  again,  and  pour 
off  into  the  flask,  continuing  the  operation  until  all  of  the 
powder  is  transferred  to  the  flask.  Fill  the  flask  with  water 
to  the  holding  mark,  pour  the  solution  into  a  dry  beaker,  mix 
thoroughly,  and  draw  off  50  cc.  for  analysis  with  a  pipette. 

Weigh  out  0.325  gm.  of  piano-forte  wire,  dissolve  it  in  a 
valve  flask  with  about  10  cc.  of  dilute  sulphuric  acid  (i  part 
H2SO  and  5  parts  H2O),  cool,  fill  the  flask  with  water,  and 


290  A   MANUAL    OF  PRACTICAL   ASSAYING. 

pour  into  a  beaker.  To  the  solution  in  the  beaker  add  the 
50  cc.  of  turbid  bleaching-powder  solution,  allowing  it  to  run 
in  slowly  from  the  pipette  and  stirring  constantly.  Dilute  to 
about  500  cc.,  and  determine  the  iron  remaining  in  the  ferrous 
form  by  means  of  a  standard  solution  of  potassium  permanga- 
nate. The  same  solution  of  permanganate  as  is  used  for  the 
determination  of  iron  (see  Part  II,  Chapter  XVI)  is  used  for 
this  purpose.  Four  atoms  of  iron  correspond  to  four  atoms 
of  chlorine,  or  56  parts  of  iron  are  equivalent  to  35.5  parts  of 
chlorine,  as  is  shown  by  the  reaction  : 

4FeSO4  +  Ca(ClO),,  Cad,  +  2H2SO  = 

2Fe2(S04)3  +  2CaCl2  +  2HaO. 

The  method  of  calculating  the  result  is  best  illustrated  by 
the  following  example :  Suppose  I  cc.  of  the  permanganate 
solution  equals  0.005  gm-  °f  iron,  and  that  16  cc.  of  the  solu- 
tion were  used  in  the  determination.  Hence  (.005  X  16  =  .08) 
0.08  gm.  of  the  0.324  gm.  of  the  iron  taken  remained  unoxid- 
ized  by  the  bleaching-powder  used.  Then  0.324  —  0.08  — 
0.244  gm.  of  iron  which  was  oxidized  by  the  bleaching-powder. 
Hence 

56  :  35.5  : :  0.244  :  0.1547  gm.  available  Cl. 

Consequently,  as  0.5  gm.   of  bleaching-powder  was  taken  for 
analysis,  the  per  cent  of  available  chlorine  =  30.94. 

Another  method  consists  in  running  50  cc.  of  the  turbid 
bleaching  powder  sulution  into  a  flask  and  adding  an  excess  of 
potassium  iodide  solution.  The  whole  of  the  available  chlorine 
displaces  an  equivalent  quantity  of  iodine ;  thus, 

Ca  (CIO),,  CaCi2  +  4KI  =  4!  +  4KC1  +  2CaO. 

which  may  be  determined  by  titration  with  a  standard  solution 
of  sodium  hyposulphite.     (See  pages  97  and  161.) 


CHAPTER  XV. 
ANALYSIS  OF  WHITE-LEAD. 

THE  white-lead  of  commerce,  when  pure,  is  a  basic  carbon- 
ate of  lead  (2PbCO3 ,  PbO2H2).  Its  value,  from  a  chemical 
standpoint,  depends  upon  the  percentages  of  PbO,  CO2,  and 
H2O  which  it  contains,  and  these  percentages  should  corre- 
spond pretty  closely  with  the  theoretical  percentages  of  the 
formula. 

In  a  white-lead  works  manufacturing  a  pure  quality  of 
white-lead  all  that  is  generally  required  is  the  percentages  of 
PbO,  CO2 ,  and  H2O. 

The  white-lead  of  commerce  is  frequently  adulterated,  the 
principal  adulterants  used  being  zinc-white  (ZnO)  and  heavy 
spar  (BaSO4).  Some  white-leads  contain  lead  sulphate  (PbSO4). 

The  best  method  of  determining  the  water  and  carbonic 
acid  is  by  direct  weight.  The  determinations  are  effected  as 
follows:  Weigh  out  from  i.o  to  2.0  grammes  of  the  white- 
lead  in  a  porcelain  boat,  and  introduce  it  into  a  piece  of  com- 
bustion-tubing. To  the  right-hand  end  of  the  tube  a  chloride- 
of-calcium  tube,  which  has  been  previously  filled  with  fresh, 
dry  calcium  chloride,  and  weighed,  is  attached.  The  calcium- 
chloride  tube  is  attached  to  a  U-tube  filled  with  freshly  ignited 
soda-lime.  The  U-tube  is  weighed  before  connecting  up  the 
apparatus.  The  U-tube  is  attached  to  another  U-tube  filled 
with  pumice  saturated  with  sulphuric  acid.  (See  determina- 
tion of  carbonic  acid,  Part  II,  Chap.  V.)  The  last  U-tube  is 
connected  with  an  aspirator.  The  left-hand  end  of  the  com- 
bustion-tube is  connected  with  a  U-tube  containing  pumice 
and  sulphuric  acid  and  a  U-tube  containing  soda-lime,  in  order 

291 


2Q2  A   MANUAL    OF  PRACTICAL   ASSAYING. 

that  the  air  passing  through  the  apparatus  shall  be  dry  and  free 
from  carbonic  acid.  After  connecting  up  the  apparatus  the 
aspirator  is  started,  and  after  it  has  run  a  few  minutes  the  boat 
containing  the  white-lead  is  gradually  heated  by  the  flame  of  a 
Bunsen  burner.  The  heat  is  gradually  increased.  After  10  to 
15  minutes'  heating  all  the  water  and  carbonic  acid  should  be 
driven  off  from  the  lead.  The  burner  is  now  removed,  and 
the  aspirator  kept  running  until  the  absorption-tubes  have 
cooled.  The  soda-lime  and  calcium-chloride  tubes  are  now 
disconnected  and  weighed,  the  increase  in  weight  of  the  cal- 
cium-chloride tube  representing  the  water  which  the  white- 
lead  contained,  and  the  increase  in  weight  of  the  soda-lime 
tube  representing  the  carbonic  acid  which  the  white-lead  con- 
tained. Should  the  lead  be  pure,  the  difference  between  the 
sum  of  the  percentages  of  carbonic  acid  and  water  and  100 
will  be  the  percent  of  lead  oxide  (PbO).  As  commercial  white- 
lead  usually  contains  some  lead  acetate,  the  residue,  after  treat- 
ment as  above  to  drive  off  water  and  carbonic  acid,  is  weighed. 
In  pure  white-lead  this  weight  may  be  taken  as  lead  oxide. 

In  the  case  of  an  impure  lead,  treat  i.o  to  2.0  grammes  of 
the  lead  with  15  to  30  cc.  of  pure,  strong  acetic  acid.  Warm 
to  effect  solution,  and  when  the  white-lead  is  thoroughly  de- 
composed, filter  through  a  small  filter  and  wash  thoroughly 
with  warm  water.  The  filtrate  will  contain  all  the  lead  which 
was  combined  as  carbonate.  This  may  be  determined  accord- 
ing to  Part  II,  Chapter  IX. 

Treat  the  residue  with  a  strong,  hot  solution  of  ammonium 
chloride,  and  filter.  The  filtrate  will  contain  the  lead  com- 
bined as  sulphate.  This  may  be  determined  according  to 
Part  II,  Chapter  IX. 

The  residue  will  contain  the  barium  sulphate,  etc.,  which 
may  be  determined  according  to  Part  II,  Chapters  I  and 
XXV. 

To  determine  the  zinc  oxide,  dissolve  i.o  to  2.0  grammes 
of  the  white-lead  in  dilute  hydrochloric  acid  and  determine 
volumetrically  with  a  standard  solution  of  potassium  ferro- 
cyanide.  (See  Part  II,  Chapter  XXI.) 


CHAPTER  XVI. 
SPECIFIC-GRAVITY  DETERMINATIONS. 

THE  specific  gravity  of  any  body  is  the  weight  of  that 
body  as  compared  with  the  weight  of  an  equal  volume  of 
another  body  which  is  assumed  as  a  standard.  The  standard 
taken  for  solids  and  liquids  is  distilled  water;  for  gases  and 
vapors,  dry  air  and  occasionally  hydrogen. 

All  determinations  of  solids  and  liquids  must  be  made  at 
the  same  temperature.  The  temperature  usually  adopted  is 
60°  Fahrenheit. 

Determinations  of  gases  and  vapors  may  be  made  at  any 
known  temperature,  and  the  volumes  reduced  to  what  they 
would  be  at  60°  Fahrenheit. 

Solids.  —  i.  The  substance  is  heavier  than  water  and  insol- 
uble in  water. 

Weigh  first  in  the  air,  suspending  the  substance  from  the 
beam  of  the  balance  by  a  piece  of  horse-hair,  and  then  in  dis- 
tilled water  whose  temperature  is  60°  F.  Let  W  '=  the  weight 
in  air,  W'=-  the  weight  in  water,  and  Sp.  gr.=  the  specific  grav- 
ity ;  then 

W 


2.  The  substance  is  heavier  than  water  and  insoluble  in 
water,  but  is  in  fragments. 

Fill  a  specific-gravity  bottle*  with   distilled  water  whose 

*  If  a  specific-gravity  bottle  is   not  at  hand,  take  a  thin-glass  flask  with  a 

narrow  neck  and  scratch  a  mark  on  the  neck.     The  flask  is  to  be  filled  to  this 

\ 

mark  in  the  determinations. 

293 


2Q4  A    MANUAL    OF  PRACTICAL  ASSAYING. 

temperature  is  60°  F.,  and  weigh  it.  This  weight  =  W.  Weigh 
the  substance  in  the  air.  This  weight  =  W.  Now  introduce 
the  weighed  substance  into  the  flask,  fill  it  with  distilled  water, 
and  weigh.  This  weight  =  W"  : 

W 
~ 


W')-  W" 

3.  The  substance  is  heavier  than  water,  but  soluble  in  it. 

Weigh  the  substance  in  the  air.  This  weight  =  W.  Now 
weigh  it  in  some  liquid  in  which  it  is  insoluble  and  whose 
specific  gravity  is  known.  This  weight  =  W.  Hence  we 
have  the  proportion,  the  specific  gravity  of  water  being  I, 

Sp.  gr.  of  liquid  :   I  =  (W  —  W)  :  W", 

in  which  W"  —  the  weight  of  water  which  would  have  been 
displaced. 

W 

Sp-  gr.  = 


4.  The  substance  is  lighter  than  water  and  insoluble  in  it. 

Weigh  the  substance  in  air.  This  weight  =  W.  Weigh  a 
piece  of  lead  of  suitable  size  in  water.  This  weight  =  W. 
Weigh  the  substance  and  the  piece  of  lead  together  in  water. 
This  weight  =  W". 

W 
Sp.  gr.  =  ^r- 


W")' 

5.  The  substance  is  lighter  than  water  and  soluble  in  it. 

Weigh  the  substance  in  the  air.  This  weight  =  W.  Intro- 
duce the  substance  into  the  flask  described  in  2,  and  fill  the 
flask  with  some  liquid  in  which  it  is  insoluble,  and  whose 
specific  gravity  is  known.  Weigh.  This  weight  =  W.  Fill 
the  flask  with  the  liquid  alone  and  weigh.  This  weight  = 
W".  Then  the  weight  of  the  liquid  displaced  =  W"  -  W  = 
A.  If  5  =  the  specific  gravity  of  the  liquid,  and^f  =  the  corre- 


SPECIFIC-GRAVITY  DETERMINATIONS.  2Q5 

sponding  weight  of  water  which  would  have  been  displaced,  we 
have 

5:  i  =  A  :  X,    and    Sp.  gr.  =  ^. 


Liquids.  —  One  of  three  methods  may  be  employed. 
6.  Weigh  some  body,  which  is  insoluble  in  water  and  in  the 
liquid,  first  in  air,  then  in  water,  and  then  in  the  liquid. 
Let  W    =  the  weight  in  air  ; 

W'  =  the  weight  in  water  ;  and 

W"  =  the  weight  in  the  liquid.     Then 

W"  -  W 


7.  The  specific-gravity  bottle  is  employed,  which  for  liquids 
is  usually  provided  with  a  hollow-glass  stopper  which  allows 
the  insertion  of  a  thermometer. 

Let  W    =  the  weight  of  the  flask  empty; 

W  —  the  weight  of  the  flask  filled  with  water; 
W"  =  the  weight  of  the  flask  filled  with  the  liquid. 

W"  -  W 


8.  By  means  of  a  hydrometer. 

The  principle  upon  which  the  hydrometer  depends  is  that 
a.  floating  body  displaces  its  own  weight  of  liquid. 

Special  hydrometers  are  made,  the  graduations  being  for 
liquids  of  different  specific  gravities,  as  the  lactometer  for  milk 
and  the  uriometer  for  urine. 

The  Baume  scale  of  graduation  is  frequently  used  in  com- 
mercial work.  It  is  purely  arbitrary.  For  liquids  heavier  than 
water  the  point  to  which  the  hydrometer  sinks  in  a  15-per-cent 
solution  of  sodium  chloride  in  water  (NaCl  15  parts,  H2O  85 
parts)  is  marked  15°.  The  point  to  which  it  sinks  in  pure 
water  is  marked  o°.  For  liquids  lighter  than  water  the  point 
to  which  the  hydrometer  sinks  in  pure  water  is  marked  10° 


296  A    MANUAL    OF  PRACTICAL   ASSAYING. 

The  point  to  which  it  sinks  in  a  lo-per-cent  sodium-chloride 
solution  (NaCl  10  parts,  H2O  90  parts)  is  marked  o°. 

The  observations  of  Baume  were  conducted  at  10°  R.  = 

54.5°  F. 

For  liquids  heavier  than  water  the  degrees  Baume"  can  be 
converted  into  specific  gravity  by  the  formula 

c  T44 

Sp.  gr.  =  -        ^0. 
144  —  & 

For  liquids  lighter  than  water  the  degrees  Baume  can  be 
converted  into  specific  gravity  by  the  formula 

Sp.  gr.  =  - 

134  4- ** 

For  specific  gravities  corresponding  to  degrees  Baume",  see 
page  297. 

Gases. — The  specific  gravity  of  a  gas  or  vapor  may  be 
determined  by  Bunsen's  method,  which  consists  in  weighing  a 
glass  globe  when  filled  with  air,  when  filled  with  the  gas,  and 
when  exhausted  by  means  of  an  air-pump.  From  the  data  so 
obtained  the  specific  gravity  can  be  readily  calculated.  As 
this  method  requires  a  powerful  air-pump  it  is  seldom  used 
except  for  scientific  work.  (See  Watts'  Dictionary  of  Chem- 
istry.) 

For  commercial  work  the  Schilling  effusion  method  is  com- 
monly used.  In  this  method  the  times  of  the  effusion  of  equal 
volumes  of  gas  and  air  through  a  fine  hole  in  a  thin  metallic 
plate  are  compared.  It  depends  upon  the  principle  that  the 
specific  gravities  of  two  gases  passing  through  such  an  opening 
are  proportionate  to  the  squares  of  the  times  of  effusion. 

Let  A  =  seconds  which  the  volume  of  air  requires  to  escape  • 
B  =  seconds  which  the  same  volume  of  gas  requires  to 

escape ; 
x  =  the  specific  gravity  of  the  gas. 

If  the  specific  gravity  of  air  =  i,  we  have 

•I  :  x  : :  A*  :  B* ;     or,     x  =  — j. 

A 


SPECIFIC-  GRA  VI T  Y  DE  TERM  IN  A  TIONS. 


297 


SPECIFIC  GRAVITIES  OF  LIQUIDS  HEAVIER  THAN  WATER.* 
TEMPERATURE  54.5°  F. 


Degrees 
Baume. 

Specific  Gravity. 

Degrees 
Baume. 

Specific  Gravity. 

Degrees 
Baume". 

Specific  Gravity. 

O 

.00000 

26 

.21129 

52 

T-53530 

I 

.00675 

27 

.22122 

53 

•55179 

2 

.01360 

28 

.23131 

54 

.56812 

3 

.02054 

29 

.24156 

55 

.58479 

4 

•02757 

30 

.25199 

56 

.60182 

5 

•03471 

31 

.26260 

57 

.61923 

6 

.04194 

32 

.27338 

58 

.63701 

7 

.04927 

33 

.28436 

59 

.65519 

8 

.05671 

34 

.29552 

60 

.67378 

9 

.06426 

35 

.30688 

61 

.69279 

10 

.07191 

36 

.31844 

62 

.71223 

ii 

.07968 

37 

•33021 

63 

•73213 

12 

•08755 

38 

.34218 

64 

.75250 

13 

•09555 

39 

.35438 

65 

•77335 

14 

.10366 

40 

.36680 

66 

•79470 

15 

.11189 

41 

•37945 

67 

.81657 

16 

.12025 

42 

.39234 

68 

.83899 

17 

.12873 

43 

•40547 

69 

.86196 

18 

•13735 

44 

.41885 

70 

.88551 

19 

.  14609 

45 

.43248 

7i 

.90967 

20 

.15497 

46 

.44638 

72 

.93446 

21 

.16399 

47 

.46056 

73 

1.95989 

22 

.17316 

48 

•47501 

74 

1.98601 

23 

.18246 

49 

.48975 

75 

2.01283 

24 

.19192 

50 

•50479 

25 

.20153 

51 

.52014 

SPECIFIC    GRAVITIES   OF   LIQUIDS   LIGHTER  THAN  WATER.f 

TEMPERATURE  54.5°  F. 


Degrees 
Baume. 

Specific  Gravity. 

Degrees 

Baume. 

Specific  Gravity. 

Degrees 

Baume. 

Specific  Gravity. 

IO 

1.  00000 

35 

0.85342 

60 

0.74432 

15 

0.96679 

40 

0.82912 

65 

0.72577 

20 

0.93571 

45 

0.80616 

70 

0.708II 

25 

0.90657 

50 

0.78443 

75 

0.691^0 

30 

0.87919 

55 

0.76385 

"  The  Baume  Hydrometer,"  a  paper  read  by  Prof.  C.  F.  Chandler  before 
the  National  Academy  of  Sciences,  at  the  Philadelphia  meeting,  1881. 

f  Ibid. 


CHAPTER   XVII. 
ANALYSIS  OF  COMMERCIAL  ALUMINIUM. 

THE  constituents  usually  required  are  silicon,  iron,  copper,, 
and  aluminium.  The  method  of  decomposition  described  is 
due  to  Rossel.* 

Three  grammes  of  the  finely-divided  metal  are  gradually  in- 
troduced  into  from  30  to  40  cc.  of  hot  caustic  potash  (30  to  40 
per  cent  solution).  The  potash  should  be  pure,  and  free  from 
silica,  alumina,  etc.  The  decomposition  is  best  effected  in  a 
platinum  dish,  as  the  caustic  potash  attacks  glass  or  porcelain. 
The  metal  dissolves,  leaving  a  black  flocculent  residue.  After 
the  decomposition  is  complete  the  solution  is  supersaturated 
with  pure  hydrochloric  acid  and  evaporated  to  dryness.  The 
dusty  dry  mass  is  heated  at  110°  C.  to  dehydrate  the  silicic 
acid,  moistened  with  hydrochloric  acid,  dissolved  in  water,  and 
the  silica  filtered  off,  washed  with  hot  water,  and  determined 
as  usual.  From  the  silica,  as  found,  calculate  the  percentage 
of  silicon. 

To  the  filtrate  from  the  silica  add  an  excess  of  sulphuric 
acid,  evaporate  to  drive  off  the  hydrochloric  acid,  and  finally 
dilute  with  cold  water  to  300  cc.  Divide  into  two  portions  of 
IOO  cc.  and  200  cc.  each. 

In  the  100  cc.  portion  (corresponding  to  I  gm.  of  the  origi- 
nal material)  determine  the  aluminium  by  nearly  neutralizing 

*Chem.  Ztg.  xxi.  4. 

298 


ANALYSIS  OF  COMMERCIAL   ALUMINIUM.  299 

the  solution  with  ammonia,  precipitating  the  iron  by  electroly- 
sis, and  finally  determining  the  aluminium  as  a  phosphate  in 
the  manner  described  in  Part  II,  Chapter  XVII. 

In  the  2OO-CC.  portion  (corresponding  to  2  gms.  of  the  orig- 
inal material)  determine  the  iron  by  reduction  with  pure  zinc 
and  titration  with  a  standard  solution  of  potassium  perman 
ganate,  in  the  manner  described  in  Part  II,  Chapter  XVI. 

For  the  determination  of  copper  dissolve  i.o  gm.  of  the 
metal  in  40  cc.  of  a  mixture  of  hydrochloric  acid  and  water 
(HC1  33  per  cent,  H2O  67  per  cent).  When  solution  is  effected, 
boil,  dilute  with  hot  water  to  250  cc.,  and  pass  sulphuretted 
hydrogen  through  the  solution  until  it  is  saturated.  The  cop- 
per sulphide  and  silicon  are  filtered  off  and  washed,  when  the 
copper  may  be  separated  from  the  silicon  and  determined  elec- 
trolytically  (see  page  157),  or  by  any  of  the  usual  methods 
(Part  II,  Chap.  XIII). 

For  the  analysis  of  titanium  and  chromium-aluminium 
alloys,  and  for  much  valuable  information  in  regard  to  the 
analysis  of  commercial  aluminium,  see  an  article  by  Hunt, 
Clapp,  and  Handy.  * 

*  Jour,  of  An.  and  App.  Chem.,  Vol.  VI,  No.  i,  Jan.  1892. 


CHAPTER   XVIII. 
ANALYSIS   OF   NATURAL   PHOSPHATES. 

THE  value  of  phosphate  rock  principally  depends  upon  the 
percentage  of  phosphoric  acid  which  it  contains.  In  addition 
to  the  phosphoric  acid  the  following  substances  affect  the  value 
of  the  material  in  the  manner  described  :  Water  and  insoluble 
matter,  which  reduce  the  percentage  of  phosphoric  acid  ;  car- 
bonates, which  increase  the  cost  of  manufacture  by  neutralizing 
their  equivalent  of  sulphuric  acid  ;  alumina  and  ferric  oxide, 
which  revert  a  portion  of  the  soluble  phosphoric  acid  and  also 
have  a  tendency  to  render  the  superphosphates  wet  and  un- 
manageable ;  and  fluorine,  which,  as  there  are  silicates  of  alu- 
minium otherwise  undecomposed  by  sulphuric  acid,  which  are 
decomposed  in  the  presence  of  fluorine,  the  otherwise  inactive 
alumina  assuming  an  objectionable  form. 

The  following  method  of  analysis  is  taken  from  an  article 
by  Dr.  T.  M.  Chatard,*  and  whilst  it  differs  somewhat  from  the 
methods  of  other  chemists,  it  is  believed  to  be  as  rapid  and 
accurate  as  any  method  which  we  have. 

Moisture. — Two  grammes  are  weighed  into  a  tared  plati- 
num crucible.  This,  with  its  lid,  is  placed  in  an  air-bath  at 
105°  C.,  and  heated  for  at  least  three  hours.  The  lid  is  then 
put  on,  and  the  crucible  is  placed  in  a  desiccator  and  weighed 
as  soon  as  cold.  The  loss  is  the  weight  in  moisture. 

*  Transactions  of  The  American  Institute  of  Mining  Engineers,  Vol.  XXI, 
page  1 60. 

300 


ANALYSIS   OF  NATURAL   PHOSPHATES.  3O1 

Combined  Water  and  Organic  Matter. — The  residue 
from  the  moisture  determination  is  gradually  heated  to  full  red- 
ness over  a  lamp,  and  then  ignited  over  the  blast-lamp.  This 
operation  is  repeated  to  constant  weight.  The  loss  (less  the 
percentage  of  carbonic  acid  as  determined  in  another  portion) 
may  be  taken  as  water  and  organic  matter.  This  method  an- 
swers for  all  technical  purposes,  but  when  minerals  containing 
fluorine  are  strongly  ignited,  a  part  of  the  fluorine  is  expelled ; 
hence,  if  more  accurate  determinations  are  required,  the  meth- 
ods given  in  Fresenius,  etc.,  should  be  followed. 

Carbonic  Acid. — The  method  by  direct  weight,  using  the 
-apparatus  described  in  Part  II,  Chapter  V,  may  be  followed. 
Many  phosphates  must  be  heated  with  dilute  acids  to  the  boil- 
ing-point to  effect  complete  decomposition  of  the  carbonates.  ' 

Insoluble  Matter. — Five  grammes  of  the  phosphate  are 
placed  in  a  beaker  or  casserole  ;  25  cc.  of  nitric  acid  (sp.  gr. 
1.2)  and  12.5  cc.  of  hydrochloric  acid  (sp.  gr.  1.12)  are  added; 
and  the  vessel,  covered  with  a  watch-glass,  is  placed  on  the 
water-bath  for  thirty  minutes.  The  solution  is  stirred  from 
time  to  time,  and  at  the  end  of  the  thirty  minutes  the  vessel 
is  removed  from  the  bath,  filled  with  cold  water,  well  stirred, 
.and  its  contents  allowed  to  settle.  The  solution  is  now  filtered 
into  a  5OO-CC.  flask,  and  the  residue  is  thoroughly  washed  with 
cold  water,  partially  dried,  and  finally  ignited  to  constant 
weight.  This  weight  may  be  considered  as  insoluble  matter. 
It  will  not  correctly  represent  the  silica,  as  the  fluorine  liberated 
during  solution  of  the  phosphate  dissolves  a  portion  of  the 
silica.  As  the  same  reaction  occurs  in  the  manufacture  of  a 
superphosphate  from  the  material,  the  result  may  be  considered 
as  a  fair  approximation  to  commercial  practice.  The  ignited 
residue  should  be  tested  for  P2O6. 

The  flask  containing  the  filtrate  is  filled  up  to  the  mark 
with  cold  water,  and  the  solution  is  thoroughly  mixed  by 
pouring  twice  into  a  dry  beaker  and  returning  to  the  flask. 

Phosphoric  Acid. — Two  portions  of  50  cc.  each  (=  0.5 
gm.  of  original  material)  are  drawn  off  with  a  pipette,  intro- 
duced into  beakers,  and  evaporated  until  the  hydrochloric  acid 


3O2  A    MANUAL    OF  PRACTICAL   ASSAYING. 

is  driven  off.  To  each  portion  150  cc.  of  molybdate  solution  is 
added,  the  solution  being  well  stirred  and  allowed  to  stand  on 
a  water-bath  until  quite  hot.  The  beakers  are  now  removed 
and  allowed  to  stand  until  the  solution  is  quite  cold.  It  is 
best  to  allow  the  solutions  to  stand  for  at  least  three  hours, 
after  which  the  yellow  precipitate  is  filtered  off  and  well 
washed  with  a  2O-per-cent  solution  of  ammonium  nitrate  con- 
taining one-thirtieth  of  its  volume  of  nitric  acid.  The  filtrate 
should  be  tested  for  PaO&  by  the  addition  of  some  molybdate 
solution  and  digestion  for  some  time.  The  funnel,  with  its 
contents,  is  now  inclined  over  the  beaker  in  which  the  precipi- 
tation was  effected,  and  the  precipitate  washed  back  into  it 
with  a  jet  of  water.  Ammonia  is  now  added,  and  on  gently 
warming  complete  solution  of  the  precipitate  should  be  ef- 
fected. Any  residue  indicates  either  incomplete  washing  or, 
under  some  circumstances,  silica.  The  solution  is  filtered 
through  the  same  filter  into  a  clean  beaker,  and  the  first  beaker 
and  the  filter  are  thoroughly  washed  with  dilute  ammonia 
water  (i  part  ammonia  and  4  parts  water).  The  solution  is 
now  boiled,  the  beaker  is  removed  from  the  heat,  and  magne- 
sia solution  is  added  drop  by  drop,  with  continual  stirring. 
The  precipitate  at  first  redissolves,  but  during  the  continual 
addition  of  the  magnesia  solution  the  solution  becomes  cloudy, 
with  a  flocculent  precipitate,  which,  as  the  stirring  continues, 
becomes  crystalline  and  subsides.  When  further  addition  of 
the  magnesia  solution  causes  no  cloudiness  and  the  crystalline 
change  is  complete,  the  beaker  is  placed  in  very  cold  water  to 
chill  its  contents  as  rapidly  as  possible.  When  perfectly  cold 
it  is  again  tested  with  a  few  drops  of  the  magnesia  solution, 
and  if  the  precipitation  is  found  to  be  complete,  about  one 
third  of  its  volume  of  strong  ammonia  is  added,  the  solution  is 
stirred  and  allowed  to  stand  three  hours.  The  precipitate  is 
finally  filtered  on  an  asbestos  felt  in  a  Gooch*  perforated  cru- 
cible, and  washed  with  the  dilute  ammonia  water.  The  wash- 
ing will  be  completed  by  the  time  the  precipitate  is  completely 

*  American  Chemical  Journal,  Vol.  I,  p.  317. 


ANALYSIS   OF  NATURAL   PHOSPHATES.  303 

removed  from  the  sides  of  the  beaker  and  transferred  to  the 
filter.  A  few  drops  of  a  strong  solution  of  ammonium  nitrate 
are  poured  on  the  precipitate,  which  is  then  carefully  dried 
and  gently  heated  until  the  fumes  of  ammonium  salts  cease  to 
come  off.  The  heat  is  now  increased,  and  as  soon  as  the  glow 
of  the  pyrophosphate  formation  has  passed  through  the  whole 
of  the  precipitate  the  crucible  is  placed  in  a  desiccator  and, 
when  cold,  weighed.  The  ignited  precipitate  is  very  white, 
and  the  difference  between  the  two  determinations  should  not 
exceed  0.05  per  cent  for  thoroughly  satisfactory  work. 

Should  a  Gooch  crucible  not  be  at  hand,  the  ammonium, 
magnesium  phosphate  can  be  filtered  onto  a  filter-paper,  and, 
after  washing,  dissolved  in  dilute  nitric  acid  into  a  small  plati- 
num dish,  the  solution  being  evaporated  to  dryness,  carefully 
ignited,  and  weighed.  A  clean  mass  is  thus  obtained,  whilst, 
should  the  precipitate  be  ignited  with  the  paper,  it  is  difficult 
to  destroy  the  carbon. 

Lime. — Evaporate  100  cc.  of  the  solution  (containing  I  gm. 
of  the  original  substance)  in  a  beaker  to  about  50  cc.,  add  10 
cc.  of  sulphuric  acid  (i  cc.  sulphuric  acid  and  4  cc.  water),  and 
evaporate  on  a  water-bath  until  a  considerable  crop  of  gypsum 
crystals  are  formed.  Cool  the  solution,  when  it  will  generally 
become  pasty  owing  to  the  additional  separation  of  gypsum. 
When  cold,  150  cc.  of  95-per-cent  alcohol  are  slowly  added, 
with  continual  stirring,  and  the  whole  is  allowed  to  stand  for 
three  hours,  with  occasional  stirring.  The  precipitate  is  fil- 
tered off,  with  the  aid  of  a  filter-pump,  into  a  distillation-flask, 
and  washed  with  95-per-cent  alcohol.  The  filter,  with  the 
precipitate,  is  gently  removed  from  the  funnel  and  inverted 
into  a  platinum  crucible,  so  that  by  squeezing  the  point  of  the 
filter  the  precipitate  falls  down  into  the  crucible  and  the  paper 
is  pressed  down  smoothly  over  it.  The  crucible  is  gently 
heated,  and  when  the  alcohol  has  burned  off  and  the  paper  is 
completely  destroyed  the  heat  is  raised  to  the  full  power  of  the 
Bunsen  burner  for  a  few  minutes,  after  which  the  crucible  is 
cooled  and  weighed.  From  the  weight  of  the  CaSO4 ,  as  thus 
determined,  the  weight  of  the  CaO  is  calculated.  Separate 


304  A    MANUAL    OF  PRACTICAL   ASSAYING. 

determinations  on  the  same  sample  rarely  differ  more  than  0.05 
per  cent. 

Ferric  Oxide  and  Alumina. — The  distillation-flask  contain* 
ing  the  alcoholic  filtrate  is  connected  with  a  condenser  and 
heated  until  alcohol  is  no  longer  distilled  over.  This  distillate, 
if  mixed  with  a  little  sodium  carbonate  and  redistilled  over 
quicklime,  can  be  used  over  and  over  again.  When  the  dis- 
tillation is  ended,  the  residue  in  the  flask  is  washed  into  a 
small  platinum  dish  and  evaporated  as  far  as  possible  on  the 
water-bath.  It  becomes  dark  brown,  owing  to  the  presence  of 
organic  matter,  which  must  be  destroyed,  since  it  prevents  the 
complete  precipitation  of  the  phosphorus  in  the  subsequent 
operation.  To  destroy  this  organic  matter,  remove  the  dish 
from  the  bath,  add  a  small  amount  of  pure  sodium  nitrate,  and 
heat  carefully  over  the  naked  flame,  keeping  the  dish  covered 
with  a  watch-glass.  If  care  be  taken,  there  will  be  no  loss  by 
spattering ;  and  the  mass  fuses  to  a  colorless,  viscous  liquid, 
cooling  to  a  glass,  which  is  readily  soluble  in  hot  water  made 
acid  with  nitric  acid.  The  solution  is  transferred  to  a  beaker, 
made  slightly  (but  distinctly)  alkaline  with  ammonia,  then 
carefully  neutralized  with  acetic  acid,  then  diluted  with  hot 
water,  brought  to  a  boil,  allowed  to  settle,  and  filtered.  After 
the  precipitate  has  been  completely  brought  on  the  filter  with 
hot  water,  the  washing  is  completed  with  a  solution  of  ammo- 
nium nitrate  (made  by  neutralizing  5  cc.  of  nitric  acid  with 
ammonia  and  diluting  to  250  cc.),  and  the  precipitate  is  dried, 
ignited  intensely,  and  weighed.  As  the  determinations  are 
made  in  pairs,  one  portion  is  used  for  the  estimation  of  phos- 
phoric acid  by  fusing  with  a  little  sodium  carbonate,  dissolving 
in  dilute  nitric  acid,  and  treating  with  molybdate  solution  as 
already  described  ;  while  the  other  portion,  also  fused  with 
sodium  carbonate,  is  dissolved  with  sulphuric  acid,  and  the  iron 
is  reduced  and  titrated  with  permanganate.  The  results  should 
not  differ  more  than  o.i  per  cent. 

Magnesia. — The  filtrate  from  the  aluminium  ferric  phos- 
phate is  evaporated  to  a  small  bulk,  made  strongly  ammo- 
niacal,  and  allowed  to  stand,  when  magnesia,  if  present,  will 


ANALYSIS  OF  NATURAL 

separate  as  the  double  salt,  and  should  be  treated  as  usual.  If 
during  the  evaporation  of  the  filtrate  (which  should  be  per- 
fectly clear  at  first)  any  flocculent  matter  separates,  it  should 
be  filtered  off  and  examined  before  proceeding  with  the  pre- 
cipitation of  the  magnesia. 

Fluorine. — Two  grammes  of  the  phosphate  are  intimately 
mixed  in  a  large  platinum  crucible  with  3  gms.  of  precipitated 
silica  and  12  gms.  of  pure  sodium  carbonate,  and  the  mixture 
is  gradually  brought  to  clear  fusion  over  the  blast-lamp. 
When  the  fusion  is  complete,  the  mass  is  spread  over  the  walls 
of  the  crucible,  which  is  then  cooled  rapidly.  The  mass  is 
detached  from  the  crucible  and  put  in  a  platinum  dish,  into 
which  whatever  remains  adhering  to  the  crucible  or  its  lid  is 
also  washed  with  hot  water.  The  contents  of  the  dish  are  now 
diluted  with  hot  water,  the  dish  is  covered  and  digested  on  the 
water-bath  until  the  mass  is  thoroughly  disintegrated.  To- 
hasten  this  the  supernatant  liquid  may  be  poured  off,  the  resi- 
due being  washed  into  a  small  porcelain  mortar,  ground  up, 
returned  to  the  dish,  and  boiled  with  fresh  water  until  no  hard 
grains  are  left.  The  total  liquid  is  then  filtered,  and  the  resi- 
due is  washed  with  hot  water.  The  filtrate  (which  should 
amount  to  about  500  cc.)  is  nearly  neutralized  with  nitric  acid 
(methyl  orange  being  used  as  an  indicator),  some  pure  sodium 
bicarbonate  is  at  once  added,  and  the  solution  (in  a  platinum 
dish,  if  one  large  enough  is  at  hand,  otherwise  in  a  beaker)  is 
placed  on  the  water-bath,  when  it  speedily  turns  turbid  through 
the  separation  of  silica.  As  soon  as  the  solution  is  warm  it  is 
removed  from  the  bath,  stirred,  allowed  to  stand  for  two  or 
three  hours,  and  then  filtered  by  means  of  the  filter-pump  and 
washed  with  cold  water.  The  filtrate  is  concentrated  to  about 
250  cc.  and  nearly  neutralized,  as  before;  some  sodium  car- 
bonate is  added ;  and  the  phosphoric  acid  is  precipitated  with 
silver  nitrate  in  excess.  The  precipitate  is  filtered  off  and 
washed  with  hot  water,  and  the  excess  of  silver  in  the  filtrate 
is  removed  with  sodium  chloride.  The  filtrate  from  the  silver 
chloride  (after  addition  of  some  sodium  bicarbonate)  is  evap- 
orated to  its  crystallizing  point,  then  cooled  and  diluted  with 


306  A   MANUAL   OF  PRACTICAL  ASSAYING. 

cold  water ;  still  more  sodium  bicarbonate  is  added,  and  the 
whole  is  allowed  to  stand,  when  additional  silica  will  separate, 
and  is  to  be  filtered  off. 

This  final  solution  is  nearly  neutralized,  as  before  ;  a  little 
sodium-carbonate  solution  is  added  ;  it  is  heated  to  boiling, 
and  an  excess  of  a  solution  of  calcium  chloride  is  added.  The 
precipitate  of  calcium  carbonate  and  fluoride  must  be  boiled 
for  a  few  minutes,  when  it  can  be  easily  filtered  and  washed 
with  hot  water.  The  washed  precipitate  is  washed  from  the 
filter  into  a  small  platinum  dish  and  evaporated  to  dryness, 
while  the  filter,  after  being  partially  dried  and  used  to  wipe  off 
any  particles  of  the  precipitate  adhering  to  the  dish  in  which 
it  was  formed,  is  burned,  and  the  ash  is  added  to  the  main 
precipitate.  This,  when  dry,  is  ignited,  and  allowed  to  cool ; 
dilute  acetic  acid  is  added  in  excess,  and  the  whole  is  evap- 
orated to  dryness,  being  kept  on  the  water-bath  until  all  odor 
of  acetic  acid  has  disappeared.  The  residue  is  now  treated 
with  hot  water,  digested,  filtered  on  a  small  filter,  washed  with 
hot  water,  partially  dried,  placed  in  a  crucible,  carefully  ignited, 
and  weighed  as  CaFQ.  The  CaF2  is  then  dissolved  in  sul- 
phuric acid  by  gently  heating  and  agitating,  evaporated  to 
dryness  on  a  radiator,  ignited  at  full  red  heat,  and  weighed  as 
CaSO4.  From  this  weight  the  equivalent  weight  of  CaF, 
should  be  calculated,  and  should  be  very  close  to  that  actually 
found  as  above,  but  should  never  exceed  it.  The  difference 
(generally  about  I  mgm.)  is  due  to  silica  which  is  precipitated 
with  the  fluoride.  The  percentage  of  fluorine  is,  therefore, 
always  calculated  from  the  weight  of  the  sulphate,  and  not 
from  that  of  the  original  fluoride.  The  results  are  very  satis- 
factory. 

For  other  methods,  as  well  as  a  complete  treatise  on  phos- 
phates, see  "  The  Phosphates  of  America,"  by  Dr.  F.  Wyatt. 


CHAPTER   XIX. 
ANALYSIS   OF   LEAD   AND    COPPER   SLAGS.* 

IN  the  following  scheme  it  is  assumed  that  the  slag  sample 
is  vitreous,  having  been  suddenly  chilled  when  taken  (see 
Part  I,  Chapter  II,  page  18).  If  such  is  not  the  case,  a  fusion 
will  be  necessary  in  order  to  effect  decomposition  of  the  slag. 
(See  Part  II,  Chapter  I,  page  83.) 

For  technical  purposes  a  partial  analysis  will  be  sufficient. 
Occasionally  a  careful  and  more  complete  analysis  may  be 
required. 

The  constituents  of  a  lead  slag  most  frequently  determined 
are  SiOa ,  FeO,  CaO,  Pb,  and  Ag;  MnO  and  ZnO  are  fre- 
quently important  constituents ;  BaO,  MgO,  and  A12O3  are 
sometimes  important  constituents  ;  Na,  K,  and  S,  whilst  present 
in  all  slags,  are  rarely  determined.  This  is  also  the  case  with 
copper  slags,  if  Cu  is  substituted  for  Pb. 

Partial  Analysis  of  Lead  Slags. — a.  Determine  the  silica 
by  treatment  of  0.5  gm.  with  water  and  hydrochloric  acid, 
boiling  the  solution  for  a  few  minutes  to  effect  solution  of  all 
except  silica,  and  filtering  as  rapidly  as  possible.  (See  Part  II, 
Chapter  XXV,  page  225.) 

b.  Determine  the  barium  by  treatment  of  0.5  gm.  with 
water,  hydrochloric  acid,  and  a  few  drops  of  nitric  and  sul- 

*  Whilst  this  scheme  is  to  some  extent  a  repetition  of  what  has  already  been 
described  in  Part  II,  the  chapter  has  been  inserted,  as  the  subject  is  of  the  ut- 
most importance  to  the  lead  and  copper  metallurgist  ;  and  the  scheme,  moreover, 
illustrates  the  manner  in  which  a  systematic  course  of  analysis  may  be  built  up 
from  the  methods  described  in  Part  II. 

307 


3O8  A   MANUAL   OF  PRACTICAL  ASSAYING. 

phuric  acids.  Evaporate  to  dryness,  take  up  with  water  and 
hydrochloric  acid,  filter,  wash,  dry,  ignite,  and  weigh  the  com- 
bined SiO,  and  BaSO4.  The  difference  between  the  weight  of 
this  precipitate  and  the  weight  of  the  SiO2,  as  determined  in  ay 
will  represent  the  weight  of  the  BaSO4. 

c.  Determine  the  lime  in  the  filtrate  from  the  SiO2  and 
BaSO4  as  obtained  in  b,  according  to  Part  II,  Chapter  XXIII, 
page  218. 

d.  Determine   the   iron    in  0.5  gm.  according   to    Part   II,. 
Chapter  XVI,  page  178. 

e.  Determine  the  manganese  in   i.o  gm.  by  treatment  with 
water,    hydrochloric   acid,    and    a   few   crystals    of   potassium 
chlorate,  boiling  to  effect  solution  and  oxidation   of  the  iron. 
Treat  and  d'etermine  according  to  Volhard's  Method.      (See 
Part  II,  Chapter  XX,  page  198.) 

/.  Determine  the  zinc  in  i.o  gm.  according  to  Part  II, 
Chapter  XIX,  page  210. 

g.  Determine  the  lead  by  fire-assay,  taking  5  or  10  gms. 
(see  Part  II,  Chapter  IX,  page  137).  Should  the  slag  be  very 
low  in  lead  (less  than  i.o#),  it  is  difficult  to  find  and  extract  the 
lead  button  from  the  slag.  In  this  case  the  following  method 
is  frequently  used :  Take  5.0  gms.  of  slag  and  weigh  out  about 
O.I  gm.  of  pure  silver,  adding  it  to  the  charge  of  slag  and  lead 
flux  in  the  crucible.  Fuse  and  pour  the  charge.  The  reduced 
lead  will  alloy  with  the  silver,  giving  a  button  which  may  read- 
ily be  found  and  detached  from  the  slag.  The  increase  in 
weight  of  the  silver  button  represents  the  weight  of  lead  in 
the  5  gms.  of  slag  taken. 

h.  Determine  the  silver  in  I  A.  T.  by  crucible  fire-assay, 
adding  sufficient  litharge  and  reducing  agent  to  obtain  a  lead 
button  of  about  4.  gms.,  which  is  cupelled.  (Part  II,  Chapter 
VII,  page  129.) 

In  the  case  of  copper  slags  proceed  in  the  same  manner, 
and  determining  the  copper  by  the  colorimetric  method.  (See 
Part  II,  Chapter  XIII,  page  159.) 

Complete  Analysis  of  Lead  Slags.— Treat  i.o  gm.  of  the 
slag  according  to  b  and  separate  the  SiOa,  BaSO4 ,  and  PbSO4J 


ANALYSIS   OF  LEAD   AND    COPPER   SLAGS  309 

washing  by  decantation  and  leaving  as  much  as  possible  of  the 
residue  in  the  casserole.  Extract  the  lead  with  ammonium 
acetate  (see  Part  II,  Chapter  I,  page  79),  and  filter  off  the  SiOa 
and  BaSO4.  After  drying,  igniting,  and  weighing  this  precipi- 
tate, fuse  it  in  a  platinum  crucible  with  sodium  carbonate,  and 
determine  the  baryta  according  to  Part  II,  Chapter  XXV,  page 
224.  The  weight  of  the  SiO2  -j-  BaSO4,  less  the  weight  of  the 
barium  sulphate  as  determined,  will  equal  the  weight  of  the 
silica.  In  very  accurate  work  the  silica  can  be  determined 
directly  by  acidifying  the  filtrate  from  the  barium  carbonate 
and  evaporating  it  to  dryness,  the  silica  being  determined  as 
usual. 

Nearly  neutralize  the  filtrate  from  the  SiO2 ,  BaSO4 ,  and 
PbSO4  with  sodium  carbonate,  add  10  to  15  gms.  of  sodium 
acetate,  and  make  a  basic-acetate  precipitation  of  the  iron  and 
alumina.  Filter  off  this  precipitate,  wash  it  with  hot  water, 
and  dissolve  it  in  a  little  dilute  hydrochloric  acid.  Reprecipi- 
tate  the  iron  and  alumina  with  ammonia  as  hydroxides  (see 
Part  II,  Chapter  XVII,  page  181  and  page  184),  filter,  and 
wash.  Dissolve  this  precipitate  with  a  little  dilute  sulphuric 
acid,  and  electrolyze,  using  mercury  for  the  cathode.  Deter- 
mine the  iron  according  to  Part  II,  Chapter  XVII,  page  i8/r 
and  the  aluminium  in  the  iron-free  solution  as  a  phosphate 
according  to  Part  II,  Chapter  XVII,  page  186. 

Combine  the  filtrates  from  the  basic-acetate  precipitate  and 
the  precipitate  of  hydroxides,  add  a  little  acetic  acid,  and  boil. 
Pass  a  current  of  sulphuretted  hydrogen  through  the  boiling 
solution  for  half  an  hour.  Filter  off  the  precipitated  zinc  sul- 
phide and  wash  with  water  containing  H2S.  (Should  the  slag 
contain  Ni  or  Co — which  is  unusual  except  in  rare  cases  of 
copper-smelting — they  will  be  precipitated  with  the  ZnS  as 
sulphides.)  The  filtrate  from  the  precipitated  zinc  sulphidp 
should  be  tested  with  H2S,  and  should  a  precipitate  form,  it 
should  be  filtered  off  and  added  to  the  first  precipitate.  Dis- 
solve the  precipitated  ZnS  with  hydrochloric  acid,  and  de- 
termine according  to  Part  II,  Chapter  XIX;  or  by  precipitation, 
as  zinc  carbonate  with  a  solution  of  sodium  carbonate,  filtra- 


3  I O  A   MA  NUAL   OF  PRA  C  TIC  A  L  A  SSA  YING. 

tion,  washing  thoroughly  with  hot  water,  and  final  ignition  of 
the  precipitate  to  ZnO,  weighing  as  such. 

Boil  the  filtrate  from  the  precipitated  zinc  sulphide,  add  an 
excess  of  bromine  water,  and  continue  to  boil  for  half  an  hour. 

Filter  off  the  precipitated  manganese  dioxide,  wash  it  thor- 
oughly with  hot  water,  boil  the  filtrate,  and  add  more  bromine 
water  to  insure  the  complete  precipitation  of  the  manganese. 
Dissolve  the  precipitated  manganese  dioxide  with  a  little  dilute 
hydrochloric  acid,  and  determine  the  manganese  according  to 
any  of  the  methods  described  in  Part  II,  Chapter  XX ;  or,  the 
precipitate  may  be  transferred  to  a  beaker  and  determined  by 
Williams'  Method.  (See  page  196.) 

Boil  the  filtrate  from  the  precipitated  manganese  dioxide 
to  expel  bromine,  render  it  alkaline  with  an  excess  of  ammonia, 
and  precipitate  the  lime  as  an  oxalate  according  to  Part  II, 
Chapter  XXIII,  page  216.  The  precipitated  oxalate  should 
be  dissolved  in  a  little  dilute  hydrochloric  acid,  the  solution  is 
rendered  strongly  alkaline  with  ammonia,  and  the  lime  is  re- 
precipitated  as  an  oxalate.  This  is  necessary  to  insure  the 
complete  separation  of  the  lime  and  magnesia.  The  lime  is 
finally  determined  according  to  Part  II,  Chapter  XXIII,  pages 
217  and  218,  either  gravimetrically  or  volumetrically. 

The  combined  filtrates  from  the  precipitated  calcium  oxa- 
late are  rendered  strongly  alkaline  with  ammonia,  the  magnesia 
is  precipitated  as  ammonium-magnesium  phosphate,  and  deter- 
mined according  to  Part  II,  Chapter  XXIV,  page  220. 

The  alkalies  are  determined  in  a  separate  portion  of  5  gms., 
according  to  Part  II,  Chapter  XXVI,  page  230. 

The  lead  is  determined  in  a  separate  portion  of  5  gms.  by 
treatment  with  water,  hydrochloric  acid,  a  few  drops  of  nitric 
acid,  and  an  excess  of  sulphuric  acid,  evaporation  to  fumes  of 
sulphuric  anhydride,  and  proceeding  according  to  Part  II, 
Chapter  IX,  page  139. 

The  sulphur  is  determined  in  a  separate  portion  of  from  2 
to  5  gms.,  proceeding  according  to  Part  II,  Chapter  II,  page  90. 

In  some  cases  the  slag  may  contain  small  amounts  of  Cu, 
Bi,  Sb,  As,  and  Sn.  In  such  a  case  it  is  necessary  to  precipi- 


ANALYSIS  OF  LEAD  AND    COPPER   SLAGS.  $11 

tate  these  elements  by  passing  a  current  of  sulphuretted  hydro- 
gen  through  the  filtrate  from  the  SiO3 ,  BaSO4 ,  and  PbSO4. 
The  precipitated  sulphides  are  filtered  off,  the  precipitate  is 
washed  with  water  containing  HSS,  and  the  different  metals  in 
this  precipitate  may  be  separated  and  determined  according  to 
the  methods  described  under  the  different  metals.  The  filtrate 
from  the  precipitated  sulphides  is  boiled,  and  the  sulphur  oxid- 
ized with  bromine  or  potassium  chlorate  before  proceeding 
with  the  analysis. 

The  same  method  will  answer  for  copper  slags,  except  that 
in  this  case  the  copper  and  other  metals  of  the  sulphuretted- 
hydrogen  group  will  have  to  be  precipitated  with  H2S,  the  pre- 
cipitated sulphides  being  filtered  out  before  proceeding  with 
the  analysis.  The  precipitated  sulphides  may  be  dissolved  in 
nitric  acid,  and  the  copper  determined  colorimetrically  accord- 
ing to  Part  II,  Chapter  XIII,  page  159. 

A  method  preferred  by  some  chemists  for  slags  containing 
baryta  is  as  follows :  Obtain  the  SiO2  and  BaSO4  by  treat- 
ment with  acids,  filtration,  etc.,  as  above.  Weigh  the  com- 
bined SiOa  and  BaSO4 ,  and  then  expel  the  silica  as  a  fluoride 
by  treatment  with  hydrofluoric  and  sulphuric  acids,  repeating 
the  treatment  until  the  weight  is  constant.  The  loss  in  weight 
equals  the  silica,  and  the  final  weight  equals  barium  sulphate, 
which  should  be  calculated  to  baryta  (BaO). 


CHAPTER   XX. 

ASSAY  OF  GOLD-ALLOYS  CONTAINING  SILVER  AND 
PLATINUM. 

PLACER  gold,  bullion,  and  old  jewelry  sometimes  contain 
platinum  when  the  ordinary  method  of  assay  cannot  be 
adopted. 

For  the  following  methods  for  the  assay  of  such  material 
the  author  is  indebted  to  J.  B.  Eckfeldt,*  Assayer  of  the  U.  S. 
Mint,  Philadelphia. 

Gold. — If  the  alloy  does  not  contain  more  than  3  per  cent 
of  platinum  the  gold  can  be  determined  as  in  the  ordinary  gold- 
bullion  assay  (see  page  246).  Should  the  percentage  of  plati- 
num be  greater  than  3,  a  smaller  proportion  of  the  alloy  should 
be  taken  for  assay,  and  sufficient  pure  gold  (the  proof  gold)  is 
added  to  bring  the  weight  up  to  1000.  For  example,  suppose 
the  alloy  contains  about  6  per  cent  of  platinum  ;  then  we  would 
weigh  out  500  parts  (=  0.25  gm.)  of  the  alloy,  add  500 
parts  (=  0.25  gm.)  of  pure  gold,  add  2000  parts  (=  I.  gm.)  of 
silver,  5  gms.  of  lead,  a  little  copper,  and  proceed  in  the  usual 
manner,  cupelling,  rolling  into  a  cornet,  and  parting  in  nitric 
acid.  The  cornet  is  boiled  in  nitric  acid  (32°  Beaume)  until  all 
action  of  the  acid  apparently  ceases,  and  is  then  boiled  for 
twenty  minutes  in  fresh  nitric  acid  (32°  Beaume).  Where  there 
is  a  large  excess  of  gold  and  silver  present  the  platinum  dis- 
solves in  the  nitric  acid.  A  proof,  made  up  as  nearly  like  the 
bullion  under  examination  as  possible,  should  be  run  with  each 
set  of  assays,  as  in  the  gold-bullion  assay.  This  is  important, 
as  there  is  invariably  some  platinum  and  silver  remaining  with 
the  gold.  Whatever  surcharge  of  platinum  and  silver  the  proof 
shows  is  to  be  deducted  from  the  weight  of  the  regular  assay. 

Platinum. — To  determine  the  platinum  make  a  second 
*  Private  communication  to  the  author. 


ALLOYS  CONTAINING  SILVER  AND  PLATINUM.      3Il 

assay  exactly  as  for  gold,  but  part  in  concentrated  sulphuric 
acid  in  place  of  nitric  acid.  The  cornet  should  be  boiled  in  the 
concentrated  acid  for  twenty  minutes,  when  the  acid  is  poured 
off  and  fresh  acid  is  added,  in  which  the  cornet  is  boiled 
twenty  minutes.  The  resulting  cornet  is  washed,  dried, 
annealed,  and  weighed,  the  weight  being  gold  and  platinum. 
Some  silver  invariably  remains  with  the  cornet,  so  it  is  neces- 
sary to  run  a  proof  made  up  exactly  as  the  regular  assay  and 
along  with  it.  Whatever  gain  in  weight  (above  the  weight  of 
gold  and  platinum  taken)  the  proof  shows  is  to  be  deducted 
from  the  weight  of  the  cornet  obtained  in  the  regular  assay. 

Silver. — The  wet  method  is  the  only  one  which  is  reliable 
for  the  determination  of  the  silver. 

One  of  the  following  methods  may  be  used : 

First  Method. — Weigh  out  500  parts  of  the  alloy  (=  0.25 
gm.),  enclose  in  2.5  to  3  gms.  of  assay  lead,  place  on  a  hot  cupel, 
and  just  fuse.  Remove  from  the  furnace,  cool,  detach  from 
the  cupel,  and  dissolve  in  nitric  acid  (26°  Beaume),  adding  to 
the  acid  the  proper  quantity  of  pure  silver  to  bring  the  total 
parts  of  silver  present  up  to  1000  (=  0.5  gm.).  For  example, 
suppose  the  approximate  fineness  of  the  bullion,  as  determined 
by  preliminary  assay,  to  be:  gold  700,  silver  150,  platinum  50, 
and  base  100,  as  500  parts  of  the  alloy  were  taken,  the  amount 
of  silver  present  would  be  75  ;  hence  75  +925  =  1000;  or  it  is 
necessary  to  add  925  parts  of  silver.  In  making  the  preliminary 
assay,  the  quantity  of  platinum  present  may  be  judged  approxi- 
mately by  the  color  the  platinum  imparts  to  the  nitric-acid 
solution.  The  assay  is  now  proceeded  with  exactly  as  in  the 
determination  of  silver  in  silver  bullion  (see  page  240),  allow- 
ance being  made,  by  deduction  from  the  result,  for  the  925 
parts  of  silver  added. 

Second  Method. — This  method  is  more  accurate  than  the 
first,  and  is  to  be  preferred  in  close  work.  Fuse  a  small 
quantity  of  potassium  cyanide  (pure  and  free  from  sujphides 
and  sulphates)  in  a  small  porcelain  crucible,  drop  into  the  fused 
mass  2  to  3  gms.  of  pure  cadmium  (or  zinc),  add  the  500  parts 
of  alloy,  and  when  fusion  is  complete  pour  out  on  a  cold  slab. 


A   MANUAL   OF  PRACTICAL  ASSAYING. 

Wash  the  button  to  free  it  from  cyanide,  dissolve  it  in  nitric 
acid  (26°  Beaum£),  adding  the  proper  quantity  of  silver  to  bring; 
the  silver  present  up  to  1000  parts,  and  proceed  to  determine 
the  silver  in  the  usual  manner  by  means  of  standard  salt  solu- 
tion. 

Alloys  containing  Indium  and  Osmium. — Occasionally 
alloys  containing  these  rare  metals  will  be  encountered.  In 
this  case  the  iridium  and  osmium  will  be  found  with  the  gold 
cornet,  and  may  be  separated  by  dissolving  the  cornet  in  aqua 
regia,  evaporating  until  the  nitric  acid  is  expelled,  diluting  with 
distilled  water,  and  filtering  off  the  iridium  and  osmium,  which 
may  be  dried  and  weighed. 

Ores. — For  the  determination  of  gold  and  platinum  in  ores 
the  ore  may  be  treated  exactly  as  in  the  gold  assay  (see  page 
258),  the  resulting  lead  buttons  being  cupelled.  The  resulting 
button  will  contain  the  gold,  platinum,  and  iridium  and  osmium, 
should  these  metals  be  present.  After  weighing,  the  buttons 
may  be  treated  exactly  as  in  the  case  of  alloys. 


PART  IV. 

CHAPTER   I. 
THE  WRITING  OF  CHEMICAL  EQUATIONS. 

IN  order  to  work  intelligently  and  to  be  able  to  calculate  the 
results  of  an  analysis  by  stoichiometry,  the  chemist  should  not 
only  thoroughly  understand  the  reactions  which  take  place  at 
each  step  in  the  analysis,  but  should  be  able  to  construct  the 
equation  which  represents  the  reaction. 

A  chemical  equation  is  the  expression  in  symbols  or  for- 
mulae of  the  changes  which  elements  or  chemical  compounds 
undergo  when  subjected  to  chemical  or  physical  influences. 
As  all  matter  is  indestructible,  these  expressions  of  change 
must  necessarily  be  equations.  A  chemical  equation  differs 
from  a  mathematical  equation  inasmuch  as  it  cannot  be  ac- 
cepted as  true  until  verified  by  experiment  ;  nor  can  it  be 
treated  in  the  same  way  as  a  mathematical  equation,  as,  for 
example,  equal  amounts  cannot  be  subtracted  from  either  side 
of  the  equation  and  leave  it  true. 

There  are  three  classes  of  chemical  equations :  Synthetical, 
Analytical,  and  Metathetical. 

Synthetical  Equations  are  those  representing  the  union 
of  elements  or  compounds  : 

2H  +  0  =  HaO, 

CaO  +  C08  =  CaCO8. 

312 


THE    WRITING   OF  CHEMICAL   EQUATIONS.  313 

Analytical  Equations  are  those  representing  the  separa- 
tion of  a  compound  into  its  constituents  : 

HaO  +  electric  spark  =  2H  +  O, 

CaCO3  +  heat  =  CaO  +  CO9. 

Metathetical  Equations  (equations  of  interchange)  are 
those  representing  the  interchange  of  elements  or  radicals,  and 
the  formation  of  new  products  : 

AgNO3  +  HC1  =  AgCl  +  HNO3. 

The  last  claim  attention  most  frequently,  and  of  these  the 
equations  of  oxidation  and  reduction  are  the  most  interesting  : 


The  laws  governing  chemical  interchange  have  not  been 
fully  determined,  but  the  two  following  exert  an  important 
bearing  on  the  results  : 

1st.  When  a  compound  can  be  formed  which  is  insoluble 
in  the  menstruum  present,  this  compound  separates  as  a  pre- 
cipitate. There  are  exceptions  to  this  rule. 

2d.  When  a  gas  can  be  formed,  or  any  substance  which  is 
volatile  at  the  temperature  at  which  the  experiment  is  made, 
this  volatile  substance  is  set  free. 

The  interchange  effected  is  always  on  terms  regulated  by 
the  quantivalence  of  the  elements  or  radicals  involved.  For 
example,  a  monad  element  or  radical  can  replace  another 
monad  element  or  radical  only  atom  by  atom.  To  effect  an 
exchange  between  a  monad  element  or  radical  and  a  dyad  ele- 
ment or  radical,  two  atoms  of  the  monad  are  required  for  each 
atom  of  the  dyad  : 

BaO  +  2HC1  =  BaCl2  +  HaO. 

In  writing  an  equation,  first  place  down  the  symbols  or 
formulae  entering  into  the  equation  in  the  first  member  of  the 
equation,  and  write  the  plus  sign  between  them.  Now  write 


3H  A   MANUAL   OF  PRACTICAL   ASSAYING. 

the  symbols  or  formulae  of  the  products  resulting  from  the 
reaction  as  the  second  member  of  the  equation.  Now  adjust 
the  factors  of  the  symbols  or  formulae  so  that  the  interchange 
will  result  in  a  true  equation.  The  data  for  the  second  mem- 
ber of  the  equation  is  either  a  matter  of  memory  or  else  must 
be  obtained  by  actual  experiment.  Very  frequently  a  knowl- 
edge of  the  conditions  which  affect  an  interchange  will  enable 
one  to  predict  by  equations  what  products  will  be  formed. 
The  adjustment  of  the  factors  is  the  important  point,  and  is 
best  illustrated  by  the  following  examples  : 

EXAMPLE  No.  I.  Required  the  construction  of  an  equa- 
tion showing  the  oxidation  of  ferrous  chloride  by  potassium 
bichromate. 

The  compounds  which  enter  into  the  reaction  are  FeCl2r 
KaCraO7,  and  HC1.  The  compounds  formed  are  Fe2Cl6,  KC1, 
CrfCl.,and  HaO. 

As  oxidation  signifies  an  increase  and  reduction  signifies 
a  decrease  in  the  quantivalence  of  an  element,  the  oxidizing 
agent,  in  exerting  its  influence,  decreases  in  quantivalence, 
whilst  the  substance  oxidized  experiences  a  corresponding 
increase  in  its  quantivalence.  Writing  out  the  equation  and 
leaving  spaces  for  the  factors,  we  have 

FeCl,+  K2CraO7  +   HC1  =    Fe2Q6+   KC1+   Cr,Cl.+   H2O. 

Now  the  iron  passes  from  the  dyad  state  to  the  tetrad 
state,  thus :  2FeO  +  O  ~  Fe2O3.  Hence  two  Fe  require 
one  O. 

One  K2Cr2O7  yields  30,  thus  :  Cr,O6  =  Cr2O3  +  36.  Hence 
6  of  the  ferrous  compound  need  I  of  the  bichromate.  Making 
the  adjustment,  we  have 

6FeCla  +  KaCr2O7  +  HC1  =  FeaCl6  +  KC1  +  Cr2Cl6  +  H2O. 

Now  if  we  arrange  the  factors  for  the  other  compounds 
according  to  the  prescribed  conditions  of  the  solution  (acid, 
alkaline,  or  neutral),  we  have 

6FeCla+  KaCr,O7+  I4HC1  =  3Fe,Cl<1+  2KC1  +  Cr2Cl,4-  ;HaO. 


THE    WRITING   OF  CHEMICAL   EQUATIONS.  315 

Testing  to  see  if  this  is  a  true  equation,  we  have 

In  the  In  the 

First  Member.   Second  Member. 

Fe  ..................     6  6 

Cl  ..................   26  26 

Cr  ...................     2  2 

0  ...................     77  7 

H  ...................    14  14 

K  ...................       2  2 

The  factors  all  balance,  and  hence  the  equation  is  correct. 

EXAMPLE  No.  2.  Required  to  construct  an  equation 
showing  the  oxidation  of  antimonous  chloride  to  antimonic 
chloride  by  potassium  permanganate. 

The  compounds  which  enter  into  the  reaction  are  Sb,Cl»r 
K2Mn2O8,  and  HC1.  The  compounds  formed  are  SbsCl,.? 
KG,  MnCl2,  and  H2O. 

Writing  out  the  equation  as  before,  and  leaving  spaces  for 
the  factors,  we  have 


SbaCl6+  K2Mn208  +  HC1=  Sb2Cl10+  KC1+  MnQ2+  H,O. 

Now  the  antimony  passes    from  the  triad  to  the  pentad 
state,  thus  : 

Sb203  +  2O  =  Sb2O5. 

One  K2MnaO8  yields  50,  thus  : 

Mn3O7  =  2MnO  +  $O. 

Hence  I  of  the  antimonous  requires  2O,  or  5  of  the  antimon- 
ous requires  loO,  or  2  of  the  K2Mn2O8.  Making  the  adjust- 
ment, we  have 

5Sb2Q6  +  2K2Mn208  +    HC1  = 

5Sb2Cl10  +  4KC1  +  4MnCl9  +    H,O. 

Arranging  the  factors  for  the  HC1  and  H2O,  we  have 

5Sb2Cl,  +  2K2Mn,08  +  32HC1  = 

5Sb2Cl]0  +  4KC1  +  4MnQ2  +  i6H80. 


316  A    MANUAL   OF  PRACTICAL  ASSAYING. 

Or  the  equation  may  be  written 
5SbCl,+  K,Mn,08+i<5HCl  =  5SbCl5+2KCl  +  2Mn 
Testing  to  see  if  this  is  a  true  equation,  we  have 

In  the  In  the 

First  Member.     Second  Member, 

Sb  ....................     5  5 

Cl  .....................   31  3i 

K  .....................       2  2 

Mn  ...................     2  2 

0  ....................     8  8 

H  .....................    16  16 

The  factors  all  balance,  and  hence  the  equation  is  correct. 

This  method  is  due  to  Prof.  Elwyn  Waller,  and  is  the 
method  taught  by  him  in  the  Columbia  College  School  of 
Mines. 

The  following  excellent  method  of  constructing  equations 
is  due  to  Otis  C.  Johnson.*  According  to  Mr.  Johnson's  defi- 
nition of  bond,  by  the  bond  of  an  element  is  meant  the  amount 
of  oxidation  it  is*  capable  of  sustaining,  and  hence  he  defines 
bond  as  an  oxidizing  force.  When  an  element  has  no  oxidiz- 
ing power  it  has  no  bonds.  When  an  element  is  a  reducing 
agent  its  bonds  are  negative. 

He  gives  the  following  rules  for  ascertaining  the  bonds  of 
an  element  : 

1st.  Hydrogen  in  combination  has  always  one  bond,  and  is 
always  positive.  (H1.) 

2d.  Oxygen  always  has  two  bonds,  and  they  are  always 
negative.  (O~n.) 

3d.  Free  elements  have  no  bonds  ;  thus  metallic  iron  (Fe°). 

4th.  The  sum  of  the  bonds  of  any  compound  is  always 
equal  to  zero.  Thus 


*  Negative    Bonds   and   Rules  for    Balancing  Equations,    Chemical  News, 
1880,  Vol.  XLII,  p.  51. 


THE    WRITING   OF  CHEMICAL   EQUATIONS. 

5th.  Acid  radicals  are  always  negative.     Thus 

Hi  N+v  Q3-vi  =  o,      and      Mg3+VI(P04)r  VI  =  O. 

6th.  Metals  in  combination  are  usually  positive.  The 
most  prominent  exceptions  to  this  rule  are  their  compounds 
with  hydrogen.  Thus 

Sb-mH3+m      and      AS-III  Hi+in 

As  the  oxidation  of  one  substance  involves  the  reduction 
of  some  other  substance,  the  number  of  bonds  gained  by  the 
one  is  lost  by  the  other. 

From  the  above  a  rule  for  writing  the  equations  of  oxida- 
tion and  reduction  is  derived,  provided  the  resulting  products 
are  known.  The  following  is  the  rule  : 

The  number  of  bonds  changed  in  one  molecule  of  each 
shows  how  many  molecules  of  the  other  must  be  taken.  The 
words  each  and  other  refer,  respectively,  to  oxidizing  and  re- 
ducing agent. 

EXAMPLE  No.  3.     Applying  this  method  to  the  problem 

FeCla  +  KaCr  A  +  HC1  =  FeaCl6  +  KC1  +  CraCl8  +  HaO, 
we  find  that 

Cra  in  the  first  member  has  12  bonds;  (Ka+nCra+xlIOT-XI7.) 
Cra  in  the  second  member  has  6  bonds.     (Cra+VI  Cle~VI.) 

Loss  =  6.     Hence  6FeCla. 

Fe  in  the  first  member  has  2  bonds  ;  (Fe+nCla"n.) 
Fe  in  the  second  member  has  3  bonds.     (Fe^^Cl,"71.) 
Gain  =  I.     Hence  iK2CraO7. 

EXAMPLE  No.  4.  Applying  this  method  to  the  problem 
SbaCl6  +  K3Mn406  +  HC1  =  Sb,Cl10  +  KC1  -f  MnCla  +  HaO, 
we  find  that 

Mna  in  the  first  member  has  14  bonds  ; 
I  Mn2  in  the  second  member  has  4  bonds. 

Loss  =  10.     Hence  ioSbC!3  or  5SbaCl8. 
Sb  in  the  first  member  has  3  bonds ; 
Sb  in  the  second  member  has  5  bonds. 
Gain  =  2.     Hence  2K2MnaO8. 


3l8  A   MANUAL   OF  PRACTICAL  ASSAYING. 

EXAMPLE  No.  5.  Required  to  construct  the  equation  for 
the  oxidation  of  ferrous  sulphate  to  ferric  sulphate  by  potas- 
sium permanganate. 

The  compounds  entering  into  the  reaction  are  K2Mn2O8 , 
FeSO4,  and  H2SO4 .  The  products  formed  are  Fe8(SO4)3 , 
KaSO4 ,  MnSO4,  and  H,O.  Writing  the  equation  and  leaving 
spaces  for  the  factors,  we  have 

FeSO4+    K8Mna08  +    H2SO4  = 

Fea(S04)3+    K8S04+    MnS04+    H2O. 
Mn2  in  the  first  member  has  14  bonds ; 
Mn2  in  the  second  member  has  4  bonds. 

Loss  =  10.     Hence  ioFeSO4. 
Fe  in  the  first  member  has  2  bonds ; 
Fe  in  the  second  member  has  3  bonds. 
Gain  =  I.     Hence  iK2Mn2O8. 

Hence  for  the  completed  equation  we  have 

ioFeSO4  +  K2Mn208  +  8H2SO4  = 

5Fe2(S04)3  +  K2SO4  +  2MnSO4  +  8H2O. 

EXAMPLE  No.  6.  Required  to  construct  the  equation 
showing  the  oxidation  of  oxalic  acid  to  carbonic  acid  by  potas- 
sium permanganate. 

The  compounds  entering  into  the  reaction  are  H  A  C2O3, 
K,Mn  A  and  H2SO4 .  The  compounds  formed  are  CO, , 
HA  MnSO  4,  and  K2SO4 .  Writing  the  equation  and  leaving 
space  for  the  factors,  we  have 

HA  C A  +    K2Mn A  +  _H,S04  = 

C02+    K2S04+    MnSO4+    HA 
Mn2  in  the  first  member  has  14  bonds, 
Mna  in  the  second  member  has  4  bonds. 

Loss  =  10.     Hence  ioH2C2O4. 
C2  in  the  first  member  has  6  bonds  ; 
Ca  in  the  second  member  has  8  bonds. 
Gain  —  2.     Hence  2K2Mn2O8. 


THE    WRITING  OF   CHEMICAL   EQUATIONS.  319 

Writing  the  equation  and  adjusting  the  factors  for  the 
HaSO4  and  HaO,  we  have 

ioH2C204  +  2KaMnaO8  +  6HaSO4  = 

2oOOa  +  2K2SO4  +  4MnSO4  +  i6H2O. 

Or  the  equation  may  be  written  (dividing  the  factors  of  each 
member  by  2), 

SH.CA  +  KaMn208  +  3H.SO,  = 

ioCOa  +  KaSO4  +  2MnSO4  +  8HaO. 

Testing  to  see  if  this  is  a  true  equation,  we  have 

In  the  In  the 

First  Member.      Second  Member. 

H 16  16 

C 10  10 

O 40  40 

K.... 2  2 

Mn   2  2 

S 3  3 

Hence  it  is  a  true  equation. 

EXAMPLE  No.  7.  Required  the  construction  of  an  equation 
representing  the  oxidation  of  MnSO4  by  KaMnaO8.  The  com- 
pounds entering  into  the  first  member  are  MnSO4,  KaMn3O8, 
and  HaO.  Those  entering  into  the  second  member  are  MnOa, 
K2SO4,  and  H2SO4.  Writing  the  equation  and  leaving  spaces 
for  the  factors,  we  have 

MnSO4+  K2MnQO8+  H2O  =  MnOa  +  KaSO4+  HaSO4. 
By  the  first  method  we  have 

MnO  +  O  =  MnO2. 
Hence  iMnO  requires  lO. 

Mn2O7  =  2MnO2  +  O3. 


32O  A   MANUAL    OF  PRACTICAL  ASSAYING. 

Hence  iK,MnaO8  yields  30.  Now  as  iMnO  requires  lO  and 
iKaMn,O8  yields  30,  we  find  that  iKaMnaO8  will  oxidize 
3MnSO4.  Hence  the  equation 

3MnSO4  +  K9MnaO8  +  2HaO  =  5MnOa  +  KaSO4  +  2H3SO4. 

By  the  second  method, 

Mn  in  the  first  member  has  2  bonds ; 
Mn  in  the  second  member  has  4  bonds. 

Gain  =  2.     Hence  2KaMn2O8. 
Mna  in  the  first  member  has  14  bonds; 
Mna  in  the  second  member  has  8  bonds. 
Loss  =  6.     Hence  6MnSO4. 

Hence  the  equation : 

6MnSO4  +  2K,Mna08  +  4HaO  =  ioMnOa  +  2KaSO4 
which  may  be  written  as  above, 


CHAPTER   II. 
STOICHIOMETRY. 

STOICHIOMETRY  is  the  arithmetic  of  chemistry.  All  that 
is  required  to  solve  the  different  stoichiometrical  problems  is  a 
knowledge  of  chemical  reactions  and  the  writing  of  chemical 
equations,  and  a  knowledge  of  the  principles  of  arithmetic. 
Most  of  the  problems  which  arise  in  the  course  of  chemical 
analysis  may  be  solved  by  simple  proportion. 

The  solution  of  the  different  problems  is  best  illustrated  by 
the  following  examples : 

Calculation  of  Percentage  from  Weight. — EXAMPLE 
No.  i. — Five  grammes  of  lead  ore  were  taken  for  assay.  A 
lead  button  weighing  2.466  gms.  was  obtained.  What  is  the 
percentage  of  lead  in  the  ore? 

5.0  (weight  taken)  :  2.466  (weight  found)  : :  TOO  :  x 
x  =  percentage  required  =  49.32. 

EXAMPLE  No.  2.  In  the  assay  of  a  zinc  ore  1.521  gms.  were 
taken  and  0.3246  gm.  of  zinc  was  obtained.  What  is  the 
percentage  of  zinc  in  the  ore  ? 

1.521  :  0.3246  : :  100  :  x ;     x  =  21.34^ 

Calculation  of  Percentage  Composition  from  Chemical 
Formula. — The  relation  existing  between  the  combining 
weights  and  the  percentages  of  the  constituents  of  a  chemical 
compound  is  best  expressed  by  a  simple  proportion  in  which 
the  first  two  terms  are  the  combining  weights  of  these  con- 
stituents and  the  last  two  terms  the  corresponding  percentages. 

321 


322  A   MANUAL    OF  PRACTICAL  ASSAYING. 

EXAMPLE    No.    3.     The   formula   for   barium   chloride  is 
Bad,  ,  2HaO  ;  required  the  percentage  of  Ba. 
We  have  the  proportion 

243.8  :  136.8  :  :  100  :  x\ 

or,  the  combining  weight  of  the  compound  is  to  the  combining 
weight  of  the  constituent  whose  percentage  is  required  as  100 
per  cent  is  to  the  percentage  required. 

In  like  manner  the  solution  of  the  following  proportions 
determines  the  percentages  of  Cl  and  H2O,  respectively  : 

243.8  :  71  :  :  100  :  x\ 
243.8  :  36  :  :  100  :  x. 

Ans.     Ba  =  56.11$  ;  Cl  =  29.12$;  H3O  =  14.76$. 

EXAMPLE  No.  4.  The  formula  for  magnesium  sulphate  is 
MgSO4,  7HaO  ;  required  its  percentage  composition  in  MgO, 
SO9,  and  HaO.  We  have  the  following  proportions: 

246  :    40  ::  IOO  :  x  ;     x  =  MgO$. 
246  :    80  ::  100  \  x\     x  =  SO3$. 
246  :  126  ::  100  :  x\     x  =  H2O$. 

Ans.     MgO  =16.26$;  SO3  =  32.52$;  H2O  =  5 


EXAMPLE  No.  5.  —  In  the  analysis  of  a  limestone  i.o  gm. 
was  taken  for  analysis,  and  a  precipitate  of  CaSO4  weighing 
0.812  gm.  was  obtained.  A  precipitate  of  Mg2P2O7  weighing 
0.385  was  also  obtained.  What  is  the  percentage  composition 
of  the  limestone  in  CaO  and  MgO? 

136  :  56  ::  0.812  :*;     x  =  0.334254  =  weight  of  CaO;     and 

i.o  :  0.334254  :  :  100  :  x\     x  =  33.43$  CaO. 
222  :  80  ::  0.385  :  x\     x  =  0.139  =  weight  of  MgO  ;     and 

i.o  :  0.139  :,  IOO  :  x\     x=  13.90$  MgO. 


STOICHIOME  TR  Y.  323 

EXAMPLE  No.  6.  Required  the  percentages  of  CaCO,  and 
MgCO3  corresponding  to  the  percentages  of  CaO  and  MgO  in 
Example  No.  5. 

56  :  100  : :  33.43  :  x ;     x  =  59.69$  CaCO,. 
40:    84::  13.90:*;     *  =  29.19$  MgCO,. 

EXAMPLE  No.  7.  How  many  grammes  of  oxygen  will  it 
take  to  convert  50  grammes  of  carbon  into  carbonic  acid  gas? 

As  each  part  of  carbon  requires  two  parts  of  oxygen,  we 
have  the  equation  • 

12  :  32  ::  50:*;     x—  133.33  g™s. 

EXAMPLE  No.  8.  How  many  grammes  of  silver  will  5 
grammes  of  sodium  bromide  precipitate  from  a  solution  of 
silver  in  nitric  acid  ?  From  the  equation, 

AgNOs  +  NaBr  =  AgBr  +  NaNO3 

•we  see  that  I  part  of  NaBr  will  precipitate  I  part  of  silver; 
hence  the  proportion 

103  :  108  1:5:*;    x  =  5.2427  gms.  Ag. 

The  Calculation  of  Factors. — In  gravimetric  analysis  the 
substance  to  be  determined  is  either  separated  in  a  state  of 
purity  and  its  weight  is  obtained  directly  (see  Examples  No.  I 
.and  No.  2),  or  by  the  operations  of  the  analysis  it  is  obtained 
and  weighed  as  a  constituent  of  a  compound  whose  formula  is 
known  (see  Examples  No.  5).  By  the  preceding  rule  the  weight 
of  the  constituent  sought  may  be  calculated.  In  Part  II  factors 
have  been  given  under  the  different  determinations  for  the  cal- 
culation of  the  weight  of  the  constituent  sought  from  the  weight 
of  the  compound  obtained  in  the  analysis.  These  factors  are 
derived  as  follows; 


324  A    MANUAL    OF  PRACTICAL  ASSAYING. 

EXAMPLE  No.  9.     Required  the  factor  for  the  calculation 
of  S  in  BaSO4. 

As  in  Examples  No.  3  and  No.  4,  we  have  the  equation 


232.8  :  32  ::  I  \x\     *  =  0.13745+, 

which  is  the  factor  for  S  in  BaSO4. 

EXAMPLE  No.  10.  Required  the  factor  for  the  calculation 
of  Sn  in  SnO3. 

We  have  the  proportion 

150:118::!:.*;     ^=0.78667, 

which  is  the  factor  required. 

EXAMPLE  No.  11.  In  the  course  of  an  analysis  nitrogen  is 
converted  into  (NH4Cl)aPtCl4,  which  precipitate  is  ignited  and 
the  weight  of  the  resulting  platinum  is  obtained.  What  factor 
will  give  the  weight  of  the  N? 

As  one  part  Pt  is  combined  with  2  parts  N,  we  have  the 
proportion 

197  :  28  ::  I  :*;    *  =  0.14213, 

which  is  the  factor  required. 

EXAMPLE  No.  12. — What  are  the  factors  for  MgO  and  P 

in  Mg,PaO7?  Ans.  MgO 0.36036. 

P 0.27928. 

The  Calculation  of  Formulae. — The  deduction  of  an  em- 
pirical formula  from  the  percentage  composition  is  the  reverse 
of  the  process  of  calculating  percentage  composition  from  for- 
mulae. 

Three  cases  may  arise. 

First  Case. — From  the  percentages  of  single  elements  in 
compounds. 


STOICHIOME  TR  Y. 


325 


EXAMPLE  No.  13.  Upon  analysis  a  substance  was  found 
to  contain  the  following  parts  in  100 : 

H 2.04 

S 32.65 

O, 65.31 

\ 

What  is  the  formula  of  the  substance  ? 

Dividing  the  percentage  of  each  element  by  its  atomic 
weight  and  reducing  the  quotients,  we  have 

H 2.04—    1=2.04—1.02  =  2 

S 32.65  —  32  =  1.02  —  1.02  =  i 

O 65.31  —  16  =  4.08  —  1.02  =  4 

Hence  the  formula  is  H2SO4. 

EXAMPLE  No.  14.  Upon  analysis  a  compound  yielded  the 
following  percentages : 

C 52.20 

H : 13.05 

O   35-00 

What  is  its  formula? 

C 52.20-12=    4.35-^4.35  =  1 

H 13-05-    1  =  13.05-^-4.35  =  3 

O 35-00  —  16  =  2.187  -=-4-35  —  0.502 

Hence,  allowing  for  error  in  the  analysis,  the  formula  is  prob- 
ably C2H6O,  which  is  the  formula  for  ethyl  alcohol- 

Second  Case. — From  the  percentages  of  groups  of  elements 
in  compounds,  isomorphous  constituents  being  absent. 

It  is  general  in  the  analysis  of  oxygen  salts  to  calculate  the 
percentages  of  oxides  and  water  equivalent  in  quantity  to  the  ele- 
ments. The  results  of  an  analysis  being  stated  in  this  manner, 
the  percentages  of  the  different  elements  may  readily  be  com- 
puted, and  from  these  percentages  the  empirical  formula  may  be 


326  A    MANUAL    OF  PRACTICAL  ASSAYING. 

calculated  by  the  preceding  rule.     The  same  result  may  be 
attained  by  the  following  shorter  course. 

EXAMPLE  No.  15. — Upon  analysis  a  substance  was  found 
to  have  the  following  percentage  composition : 

H2O 51-20 

'SO3 32.53 

MgO 16.24 

What  is  its  chemical  formula? 

Dividing  each  constituent  by  its  molecular  weight  and  re. 
ducing  the  quotients  to  their  simplest  relations  in  whole  num- 
bers, we  have 


H2O.. 51-20 

sos 32.53 

MgO 16.24 


1 8  =  2.844+ 
80  =  0.40066+ 
40  =  0.4006 


0.4006  =  7.09 
0.4006  =  i  .00 
0.4006  =  i  .00 


Hence,  allowing  for  error  in  the  analysis,  the  probable  rational 
formula  is  MgOSO3 ,  /H2O.  Rearranging  the  order  in  which 
the  symbols  of  the  elements  stand,  we  have  the  strictly  em' 
pirical  formula  MgSH14On. 

Having  obtained  the  empirical  formula  of  a  compound,  its 
rational  formula  may  be  obtained  by  making  any  reasonable 
supposition  regarding  its  chemical  constitution  and  arranging 
the  atoms  conformably.  For  example,  in  the  above  case, 
allowing  lO  to  the  Mg  we  have  loO  remaining  and  I4H. 
Assuming  that  the  H  is  combined  with  O  as  water  of  crystalli- 
zation we  have  7H2O,  which  still  leaves  30  to  be  combined 
with  the  S  as  SO3.  Hence  the  formula  MgOSO3 ,  ;H2O,  or 
MgSO4,;H0O. 

Third  Case. — From  the  percentages  of  groups  of  elements 
in  compounds,  isomorphous  constituents  being  present. 

In  the  deduction  of  formula  it  should  be  remembered  that 
closely  related  radicals  may  replace  each  other  in  all  propor- 
tions. This  is  especially  true  of  the  basic  metals.  Generally, 
elements  of  like  valence  are  found  replacing  one  another;  but 


STOICHIOME  TR  Y. 


327 


in  some  cases  equivalent  amounts  of  elements  having  different 
valence  replace  each  other. 

EXAMPLE  No.  16.     Penfield  *  found  by  analysis  of  triphy 
lyte  the  following  composition : 


PO  

.  .  4/1.76 

FeO  

26  40 

MnO  

.  17.84 

CaO  

.    O.24 

MgO   . 

.    O.47 

Li  O  

.    Q.^6 

Na2O  

....  o.  3  5 

tLO.. 

.    0.42 

What  is  the  formula  for  the  mineral? 

Molecular  Weights.     Mol.  Ratio. 


99.84 


Atomic  Ratio. 


po  

,  ,  /MT76  - 

-  142 

-     72 
-     71 
-      56 
-     40 

-      30 
-     62 

=  •315  x 

=  .366 

=5=  .251 

=   .004 
=  .OI2 

=  .312  x 
=  .005  x 

2  =  P          .630 

=  Fe      .366^ 
=  Mn    .251  1 
=  Ca      .004  | 

=  Mg     .OI2'J 

2  =  Li      .624  | 
2  =  Na     .010  ) 
O     2x2; 

FeO   .  .  . 

.  .  .   26.40  - 

MnO..., 

.  17.84  - 

CaO  .  ,  .  . 

.    O.24  - 

MeO 

O  47  - 

LiO   . 

.     Q.^6  - 

NaO 

O.3^  - 

HX>.. 

.    0.42 

R"  -633 
R'  -634 


In  this  case  the  small  amount  of  water  may  be  disregarded. 
The  atomic  ratio  column,  with  the  adjoined  symbols,  is  the 
empirical  formula. 

As  is  to  be  expected,  when  isomorphous  constituents  are 
present,  the  number  of  different  atoms  are  not  in  any  simple 
ratio.  Hence  it  remains  to  unite  the  atoms  of  such  elements 
as  are  supposed  to  be  capable  of  mutually  replacing  each  other, 
and  ascertain  if  the  numbers  thus  obtained  are  in  any  simple 
proportion.  For  this  purpose  let  R"  represent  one  atom  of 
any  dyad  basic  metal  and  R'  one  atom  of  any,  nomad  basic 


*Fresenius,  Quantitative  Chemical  Analysis,  p.  847. 


328  A    MANUAL    OF  PRACTICAL   ASSAYING. 

metal  present.  The  atomic  ratio,  obtained  as  above,  is  ex- 
pressed by  the  formula  R"6ilR'M4P6,0OaM, ,  or  dividing  by  630, 
almost  exactly  by  R"R'PO4,  which  is  equal  to 

/CL   p" 

(PO)'"£-O>K  , 

X0— R' 

anhydrous  normal  lithium  phosphate  in  which  iron  is  partially 
replaced  by  manganese,  magnesium,  and  calcium ;  and  lithium 
to  a  slight  extent  by  sodium. 

Omitting  oxygen  from  the  above  calculation,  we  have 
R"R'P.  Referring  to  the  percentage  computation,  it  is  seen 
that  two  P  require  five  O ;  two  R'  one  O ;  one  R"  one  O. 
Doubling  R"R'P  and  appending  to  each  constituent  the  re- 
quired oxygen  atoms,  we  have  R"aO8R'2OP2O6  =  R",R'2PaO8 
=  R"R'PO4,  as  before. 

EXAMPLE  No.  17.  A  lead  blast-furnace  slag  upon  analysis 
gave  the  following  percentage  composition : 

SiO3 , 36.0 

FeO 28.8 

CaO 28.0 

AlA 7-6 

100.4 

Required  a  formula  which  represents  the  composition  ? 

Molecular  Ratio.     Atomic  Ratio. 

SiO, 36.0-    60  =  .6      SiO2  .6 

Fe° 28.8-    72^.4       Fe     .41          f 

CaO 28.0-    56=1.5       Ca      .5  [* 

A1908 ;.6  _  102  =  .075  Al      .15  R'"  .15 

Dividing  this   atomic  ratio  by  0.15,   we   obtain  the  formula 

R."R'"Si4,  or  (R,"02)6(R2'"03)(Si02)8  =  (R"O)12(R/"O3)(SiO21), 

Calculations  involved  in  the  Making-up  and   Use   of 

Volumetric    Solutions.— EXAMPLE   No.    18.     Required   the 


S  TOICHIOME  TR  Y.  3  29 

amount  of  sodium  bromide  necessary  to  add  to  water  in  order 
to  make  a  solution  of  which  i  cc.  will  exactly  precipitate  o.oi 
gm.  of  silver? 

From  the  equation 

AgNO3  +  NaBr  =  AgBr  +  NaNO3 

we  see  that  i  atom  of  Br  precipitates  i  atom  of  Ag.  Hence 
the  proportion 

108  :  103  : :  O.OI  :  x ;     x  =  0.009537 ; 

108  being  the  atomic  weight  of  Ag  and  103  being  the  molecular 
weight  of  NaBr.  Consequently  if  1000  cc.  is  the  quantity  of 
standard  solution  required,  weigh  out  9.537  gms.  of  pure  dry 
sodium  bromide,  dissolve,  and  dilute  to  1000  cc.  with  distilled 
water. 

EXAMPLE  No.  19.  Upon  trial  of  the  sodium-bromide  solu- 
tion as  made  up  in  the  preceding  example  each  cc.  was  found 
to  only  precipitate  0.00956  gm.  of  Ag.  Required  the  amount 
of  the  salt  which  should  be  added  to  1000  cc.  so  that  each  cc. 
will  precipitate  exactly  o.oi  gm.  of  Ag?  As  9.537  gms.  of 
NaBr  were  taken  in  making  up  1000  cc.  of  the  solution,  we  have 
the  proportion 

0.00956  :  o.oi  : :  9.537  :  x\     x  =  9.9759  gms., 

which  is  the  amount  of  sodium  bromide  which  should  have 
been  taken.  Hence  9.9759  —  9-537  ~  0.4389  gm.  of  NaBr  to 
be  added  to  each  looo  cc.  of  the  solution  to  make  it  normal. 

EXAMPLE  No.  20.  An  acid  solution  of  ferrous  sulphate 
contains  0.215  gm.  of  iron.  How  many  cc.  of  a  solution  of  po- 
tassium permanganate  containing  o.oi  gm.  of  K2Mn3O8  in  each 
cc.  will  be  required  to  convert  the  ferrous  sulphate  to  ferric 
sulphate? 

By  reference  to  the  equation  representing  the  oxidation 
(see  Part  IV,  Chapter  I)  we  see  that  I  molecule  of  K2Mn3Oe 
-will  oxidize  10  molecules  of  ferrous  iron.  The  molecular 


33°  A   MANUAL   OF  PRACTICAL  ASSAYING. 

weight  of  loFe  is  560  and  the  molecular  weight  of  iKaMn,Q 
is  316.2;  hence 

560  :  316.2  ::  0.215  :  x;     #=0.1214. 

Now,  as  each  cc.  of  the  solution  contains  o.oi  gm.  K2Mn2O.  and 

0.1214 
0.1214  gm.  are  required,  we  will  require -  =  12.14  cc.  of 

the  solution. 

EXAMPLE  No.  21.  A  solution  of  potassium  permanganate 
was  found  to  be  of  such  a  strength  that  each  cc.  was  equivalent 
to  (would  oxidize)  0.0093  gm.  of  iron.  What  is  the  value  of 
the  solution  in  terms  of  manganese? 

By  reference  to  the  equation  for  the  precipitation  of  man- 
ganese by  potassium  permanganate  (see  Part  IV,  Chapter  I). 
we  see  that  I  molecule  of  K2Mn2O8  will  precipitate  3  atoms  of 
Mn,  whilst  each  molecule  of  K2Mn2O8  will  oxidize  10  molecules 
of  Fe.  Hence  the  proportion 

560  :  165  : :  0.0093  :  x\     x  =  0.00274; 

560  being  the  molecular  weight  of  loFe  and  165  being  the 
molecular  weight  of  3Mn. 

EXAMPLE  No.  22.  Having  prepared  and  standardized  the 
following  solutions,  required  the  equivalent  of  the  iodine  solu- 
tion in  terms  of  sulphur: 

A  solution  of  potassium  bichromate  of  which  I  cc.  =  0.005 
gm.  Fe. 

As  I  equivalent  of  K2Cr2O7  oxidizes  6  equivalents  of  Fe,  we 
have  the  proportion 

336  :  294.5  : :  0.005  •  *  \     *  =0.004382 ; 

or,  each  cc.  of  the  bichromate  solution  contains  0.004382  gm, 
of  K2Cr,07. 

A  solution  of  iodide  of  potassium  was  prepared  by  dissolv- 
ing i  gm.  of  pure  KI  in  300  cc.  of  water  and  5  cc.  of  HC1.  To 
this  solution  25  cc.  of  the  bichromate  solution  was  added. 


S  TOICHIOME  TRY.  331 

Now,  as  294.5  parts  of  K2Cr2O7  will  liberate  761.1   equivalents 
of  iodine  (see  Part  II,  Chapter  II),  we  have  the  proportion 

294.5  :  761.1  :  :  0.10955  :  x;     x  —  0.28312; 

or,  the  25  cc.  of  bichromate  will  liberate  0.28312  gm.  of  iodine. 

Upon  the  addition  of  sodium-hyposulphite  solution  to  this 
solution  containing  0.28312  gm.  of  free  iodine,  24  cc.  were  re- 
quired to  decolorize  the  solution.  Hence  each  cc.  of  the  hypo- 
sulphite solution  contains  sumcien'  NaHS2O3  to  react  on 
0.0118  gm.  of  iodine. 

Ten  cc.  of  the  hyposulphite  solution  were  then  drawn  off, 
diluted  with  water,  a  few  drops  of  starch  solution  were  added, 
and  the  iodine  solution  to  be  standardized  was  run  in  until  the 
blue  color  was  destroyed,  20  cc.  being  used. 

As  10  cc.  of  the  hyposulphite  solution  would  react  on  o.i  180 
gm.  of  iodine,  each  cc.  of  the  iodine  solution  contains  0.0059 
gm.  of  iodine.  From  the  equation 


we  have  the  proportion 

253.7  :  32  :  :  0.0059  :  x\     *  =  0.000744; 

or,  each  cc.  of  the  iodine  solution  is  equivalent  to  0.000744 

gm.  S. 

Calculation  of  the  Results  of  Indirect  Analyses.  —  EX- 

AMPLE No.  23.  In  the  analysis  of  a  mineral  containing  both 
calcium  and  strontium  the  Ca  and  Sr  were  separated,  converted 
into  CaCO3  and  SrCO3  ,  and  the  mixed  carbonates  were  weighed 
together.  Subsequently  the  carbonic  acid  was  determined. 
The  weight  of  the  mixed  carbonate  was  0.935  gm.  and  the 
weight  of  the  carbonic  acid  which  the  mixed  carbonates  con- 
tained was  0.362  gm.  Required  the  corresponding  weights  of 
CaO  and  SrO. 

Mol.  Wt.  C02.      Mol.  Wt.  SrC03.  Wt.  COa. 

44  :          147-5         ••        0-362      :      x\     *=  1.21352. 


332  A    MANUAL    OF  PRACTICAL  ASSAYING. 

If,  therefore,  the  whole  of  the  carbonic  acid  were  combined 
with  strontia,  the  weight  of  the  carbonate  would  be  1.21352 
gms.  The  difference  (1.21352  —  0.935)  =  0.27852  is  propor- 
tional to  the  calcium  carbonate  present,  which  is  calculated 
as  follows : 

The  difference  between  the  molecular  weight  of  SrCO3  and 
the  molecular  weight  of  CaCO3  (47.5)  is  to  the  molecular  weight 
of  CaCO,  (100)  as  the  difference  found  is  to  the  calcium  car- 
bonate  contained  in  the  mixed  salt ;  or, 

47.5:100:10.27852:^;     ^  =  0.5864. 

Therefore  the  mixture  contains  0.5864  gm.  CaCO3  and  0.3486 
gm.  SrCO,. 

Calculations  involved  in  the  Analysis  of  Gases. — Reduc- 
tion of  the  Volume  to  what  it  would  be  in  the  Normal  State. — 
The  tension,  and  therefore  the  volume  of  the  gas,  depends 
upon  :  The  pressure ;  the  temperature  ;  the  state  of  moisture. 

Gases  are  measured  in  their  condition  at  the  time  at  which 
the  measurement  is  made ;  that  is,  at  the  atmospheric  pressure 
as  indicated  by  the  barometer  and  at  the  temperature  as  indi- 
cated by  the  thermometer,  and,  as  the  confining  liquid  is  gen- 
erally water,  in  a  state  of  complete  saturation  with  moisture. 
Hence  it  is  necessary  to  reduce  the  volume  of  the  gas,  as 
measured  under  known  but  varying  conditions,  to  the  volume 
which  it  would  have  at  the  normal  barometric  pressure  of  760 
millimetres,  at  the  normal  temperature  of  o°  C.,  and  in  the  dry 
state. 

According  to  Boyle's  law,  the  volume  of  a  gas  varies  in- 
versely as  to  the  pressure  to  which  it  is  subjected.  If 

F0  =  the  volume  at  the  normal  pressure  sought; 
V=  the  volume  at  the  barometric  pressure  B] 

B  =  the  state  of  the  barometer  at  the  time  of  the  observa- 
tion,— we  have 


S  TOICHIOME  TRY.  333 


The  expansion  by  heat  of  a  gas  is  ^¥  of  its  volume  at  o° 
for  each  degree  C. 

Hence,  if  a  gas  measures  273  cc.  at  o°  C.,  it  will  measure 
273  +  *  cc.  at  r  C.     If 

FO  =  the  volume  of  the  gas  at  the  normal  temperature  ; 

F=  the  volume  of  the  gas  at  the  temperature  /; 

/  =  the  temperature  at  the  time  of  observation,  —  we  have 


273+' 

If  a  gas  is  saturated  with  moisture  by  contact  with  water, 
it  always  takes  up  the  same  quantity  of  water  under  the  same 
conditions.  This  water  is  itself  transformed  into  the  gaseous 
state,  and  exerts  a  certain  pressure  called  the  tension  of  aqueous 
vapor.  This  tension  of  the  aqueous  vapor  increases  as  the  tem- 
perature increases.  This  tension  has  been  determined  experi- 
mentally (see  Tables),  and  must  be  deducted  from  the  observed 
barometric  pressure  in  each  determination. 

If  B  —  f  •=.  the  corrected  barometric  pressure,  we  have  the 
following  formula,  which  embraces  all  corrections : 


-  ,., 

(273  +  ^x760  ' 

The  reduction  of  the  volume  of  a  gas  to  the  normal  state 
may  be  omitted  in  cases  where  only  approximate  results  are 
required,  and  also  in  determinations  which  are  made  rapidly, 
as  material  changes  of  pressure  and  temperature  are  not  to  be 
expected. 

To  reduce  the  volume  of  a  gas  from  the  normal  state  to 
that  which  it  would  occupy  at  a  different  pressure  and  tem- 
perature, and  in  a  state  of  complete  saturation  with  moisture, 
we  have  the  equation 


EXAMPLE  NO.  24.     A  gas  measured  over  water  occupied  a 
volume  of  100  cc.,  the  barometric  pressure  being  730  mm.  and 


334  A   MANUAL   OF  PRACTICAL   ASSAYING. 

the  temperature  being  25°  C.     What  will  be  its  volume  at  760 
mm.  and  o°  C.  ? 

Substituting  in  formula  A,  we  have 

IOQ  X  273  X  (730 -23.58) 
(273  +  25)  X  760 

EXAMPLE  No.  25.  The  volume  of  a  dry  gas  at  760  mm. 
pressure  and  o°  C.  was  100  cc.  What  volume  would  it  occupy 
if  saturated  with  moisture  at  a  temperature  of  40°  C.  and  740 
mm.  barometric  pressure? 

Substituting  in  formula  B,  we  have 

100(273+40)760  =          2  cc 
273(740  -  55) 

Calculation  of  Percentage  by  Weight  from  the  Volume. — 
Having  measured  the  volume  of  the  gas  and  reduced  this 
volume  to  the  normal  state  (Examples  No.  24  and  No.  25),  its 
percentage  by  weight  may  be  obtained  by  means  of  Table  IV, 
showing  the  absolute  weight  of  gases  (Tables). 

EXAMPLE  NO.  26.  What  is  the  percentage  by  weight  of 
nitrogen  in  a  substance  of  which  i.o  gm.  yielded  40  cc.  of  dry 
nitrogen  gas  at  o°  C.  and  760  mm.  barometer? 

By  Table  IV  we  see  that  1000  cc.  of  dry  nitrogen  at  o°  C. 
and  760  mm.  weighs  1.2562  gms. ;  hence 

1000  :  1.2562  : :  40  :  x;     x  —  0.05025  gms. ; 
and 

i.o  :  0.05025  : :  100  :  x ;     x  =  5.025$  N. 

EXAMPLE  No.  27.  One  gramme  of  a  substance  upon 
analysis  yielded  150  cc.  of  carbonic-acid  gas,  the  gas  being 
measured  at  22°  C.  and  750  mm.  barometer.  What  is  the  per- 
centage of  carbon  in  the  substance? 

Substituting  in  equation  A,  we  have 

150(273  X  730.3)  = 

'  (273  +  22)760  I34'°5  cc- 


S  TOICHIOME  TRY.  335 

By  Table  IV  we  find  that  1000  cc.  of  dry  COS  in  the  normal 
state  weighs  1.9663  gms. ;  hence 


1000  :  1.9663  : :  134.05  :  x\    x  =  0.2636  gm. ; 
and 

i.o  :  0.2636  : :  100  :  x\    x  =  26.36$  CO,; 
and 

44  :  12  ::  26.36  :  x\    x  =  7.18$  C. 

When  the  percentages  of  the  different  gases  are  deter- 
mined by  volume  (see  Part  III,  Chapter  XI),  the  calculation 
will  be  as  follows,  no  corrections  for  barometric  pressure,  tem- 
perature, etc.,  being  necessary: 

% 
Analysis  of  Coal  Gas. 

Volume  of  Gas  employed,  100  cc. 

A.  Estimation  of  the  Absorbable  Constituents. 

After  absorption  with  caustic  potash 98.6  cc. 

Decrease  of  volume 1.4"   =  1.4  volume  per  cent 

After  absorption  by  bromine  water  and  removal  of  carbon  dioxide. 

of  the  bromine  vapor  by  caustic  potash 94.8  " 

Decrease 3.8  "   =3.8   per   cent   ethy- 

lene,    propylene, 

After  absorption  by  fuming  nitric  acid  and  re-  butylene. 

moval  of  the  nitrous  fumes  by  caustic  potash.  93.8  " 

Decrease i.o  "   =  i.o  per  cent  benzine 

vapor. 

After  absorption  by  potassium  pyrogallate 93.5  " 

Decrease 0.3  "   =  0.3  percent  oxygen. 

After  absorption  by  cuprous  chloride 87.0  " 

Decrease 6.5  "  =6.5  per  cent  carbon 

monoxide. 
Kon-absorbable  remainder 87.0  " 


336  MANUAL   OF  PRACTICAL   ASSAYING. 

B.  Estimation  of  the  Hydrogen  and  Methane. 

A  portion  of  the  unabsorbable  remainder  is  now  drawn  off 
into  a  eudiometer,  mixed  with  oxygen,  and  exploded. 

Volume  of  unabsorbable  remainder  drawn  off  into 
eudiometer  (corresponding  to  35  cc.  of  the  orig- 
inal gas) 30.5  cc. 

Volume  before  explosion  (57  cc.  of  oxygen  added)..  87.5     " 

Volume  after  explosion 50.0     " 

Decrease  (HaO) 37.5     " 

Corresponding  to  hydrogen 25.0    " 

Oxygen 12.5     '* 

Volume   after  absorption  of   carbon    dioxide  with 

potassic  hydrate 43.0    " 

Decrease  (CO2) 7.0     " 

Corresponding  to  carbon 2.33  " 

"oxygen 4.66" 

Oxygen  added 57-OO  " 

Oxygen    combined   as  water  and   carbon   dioxide 

(12.50  +  4.66) 17.16  «• 

Oxygen  remaining  after  treatment 39. 84  " 

Volume  of  oxygen  and  nitrogen   remaining  after 

treatment 43.00  " 

Nitrogen  (43.00  —  39.84) 3. 16  "  =  9.03^  nitrogen 

Carbon  calculated  to  methane  (CH 4) 11.65   "  =  33-28$  methane 

Total  hydrogen 25.00  " 

Less  hydrogen  calculated  to  methane 9.32  " 

Hydrogen 15.68  "  =44. 80^  hydrogen 


CHAPTER    III. 
THE  CALCULATION  OF  LEAD  BLAST-FURNACE  CHARGES. 

THE  calculation  of  a  lead  blast-furnace  charge  is  a  more 
or  less  complex  problem,  owing  to  the  many  different  points 
which  have  to  be  taken  into  consideration.  Consideration 
must  be  given  to  the  following : 

First.  The  charge  must  be  calculated  so  as  to  produce  a 
slag  which  will  be  good  from  both  a  metallurgical  and  an 
economic  standpoint.  A  good  metallurgical  slag  is  one  which 
is  fusible,  is  adapted  to  the  ores  to  be  treated,  should  keep 
the  furnace  in  good  condition,  should  allow  of  a  good  separa- 
tion of  matte  and  speisse  from  the  slag,  and  should  be  low  in 
both  lead  and  silver.  An  economic  slag  is  one  which  will  fulfil 
the  above  conditions  and  at  the  same  time  allow  an  economic 
mixture  of  the  ores  to  be  treated  and  require  a  minimum 
amount  of  costly  flux.  For  example,  at  the  present  smelting 
centres  of  the  West  the  majority  of  the  ores  received  are  d-ry 
silicious  ores,  and  these  are  the  ores  in  which  there  is  the 
largest  margin  of  profit.  Lead,  iron,  and  lime  are  necessary 
fluxes  which  have  to  be  added  to  the  charge  to  produce  the 
proper  amount  of  bullion  and  the  proper  slag,  and  these  fluxes 
are  more  or  less  costly,  as  they  have  to  be  purchased  at  a  price 
which  allows  little  or  nothing  for  smelting,  and  for  every  pound 
of  flux  added  to  the  charge  one  pound  less  of  ore,  in  which 
there  is  a  profit,  can  be  added.  The  amount  of  time,  fuel, 
labor,  etc.,  expended  in  smelting  a  pound  of  flux  is  the  same 
as  that  expended  in  smelting  a  pound  of  ore.  The  following 
table  gives  the  different  type  slags  which  are  good  metallurgi- 
cal slags. 

337 


338 


A   MANUAL    OF  PRACTICAL  ASSAYING. 


Slag  A  is  a  good  slag,  which  has  been  used  in  Utah  and 
elsewhere  for  several  years.  It  is  especially  adapted  to  ores 
carrying  considerable  alumina.  This  slag  cannot  be  success- 
fully' made  with  impure  ores  having  a  high  percentage  of  zinc. 

Slag  B  is  a  favorite  slag  with  Utah  smelters,  and  is  one  of 
the  best  slags  which  we  have,  being  more  fusible  and  driving 
faster  than  A.  This  slag  is  not  adapted  to  ores  containing 
high  percentages  of  zinc, 

TABLE   OF   TYPE   SLAGS. 


Notation. 

SiOa. 
Per  Cent. 

FeO. 
Per  Cent. 

CaO. 
Per  Cent. 

ZnO. 
Per  Cent. 

A 

«5C 

28 

28 

B  

•34 

34 

24 

c  

34 

34 

17 

7 

D 

ao 

J.O 

2O 

E 

Of) 

48 

^12 

F  

28  to  30 

54 

6 

Slag  C  is -a  favorite  type  with  Colorado  smelters,  as  it  runs 
ivell  with  high  zinc  charges,  which  is  generally  the  rule  in 
Colorado.  As  the  per  cent  of  zinc  on  the  charge  decreases  the 
per  cent  of  lime  is 'raised,  the  slag  more  nearly  approaching 
type  B  in  composition.  Types  B  and  C  really  belong  to  the 
same  general  type,  and  are  very  similar  in  many  of  their  physi- 
cal properties. 

Type  D  is  a  most  excellent  slag1,  generally  known  as  "the 
half  slag."  This  slag  was  formerly  much  used  by  Colorado 
and  Utah  smelters,  but  owing  to  the  scarcity  of  iron  in  the 
ores  of  late  years  it  is  seldom  used  now. 

Slag  E  is  what  is  generally  known  as  "  the  quarter  slag," 
and  was  much  used  in  the  early  days  of  smelting  in  Utah  and 
Leadville  when  the  ores  were  generally  oxidized  ores  carrying 
a  high  per  cent  of  ferric  oxide.  It  is  a  most  excellent  slag, 
and  answers  all  metallurgical  purposes,  but  can  only  be  run  in 
exceptional  cases  owing  to  the  prevailing  scarcity  of  iron  in  the 
ores. 

Slag  F  is  not  as  good  a  slag  as  any  of  the  foregoing,  and  is 


CALCULATION   OF  LEAD   BLAST-FURNACE    CHARGES.     339 

only  to  be  recommended  in  certain  rare  and  isolated  places 
where  there  is  a  large  excess  of  iron  in  the  ores,  and  silicious 
ores  are  not  available. 

In  all  of  the  above  types  the  sum  of  the  SiO2 ,  FeO,  and 
CaO  is  considered  as  making  about  90  per  cent  of  the  slag 
constituents.  This  will  be  found  to  be  the  case  except  when 
the  ores  contain  much  ZnO  and  A12O3,  MnO  being  considered 
as  FeO  and  MgO  and  BaO  as  CaO.  Up  to  certain  limits  MnO 
will  satisfactorily  replace  FeO,  and  the  same  may  be  said  of 
MgO  and  BaO  as  regards  CaO.  Too  much  MnO  (above  7 
per  cent  or  8  per  cent)  seems  to  have  a  tendency  to  carry  silver 
into  the  slag  and  too  much  MgO  or  BaO  (above  4  per  cent  or 
5  per  cent  in  high  lime  slags)  has  a  tendency  to  render  the 
slags  more  infusible  and  pasty,  and  is  liable  to  cause  trouble 
in  the  furnace. 

Second.  The  charges  must  be  calculaed  with  regard  to  the 
ore  supply  on  hand,  and  what  may  be  expected  from  the  daily 
receipts  of  ore  ;  that  is,  the  products  of  the  roasting  and  fusing 
furnaces,  and  the  raw  smelting  ore  coming  to  the  works,  must  be 
used  in  about  the  proportions  in  which  they  exist,  so  as  to  not 
have  a  surplus  of  certain  ores  or  products  on  hand.  Hence  the 
"metallurgist  must  keep  posted  as  to  the  condition  of  the  ore 
market,  and  the  ore-buyer  must  keep  posted  as  to  the  require- 
ments of  the  metallurgist. 

Third.  The  charge  must  not  only  be  so  calculated  that  we 
will  have  a  sufficient  amount  of  lead  on  the  charge,  but  also  so 
that  the  bullion  will  be  of  the  proper  grade.  In  the  early  days 
of  smelting  in  this  country  a  2O-per-cent  lead-charge  was  not 
unusual,  while  at  the  present  time  a  12-per-cent  charge  may 
be  stated  as  the  average  charge.  As  low  as  a  6-per-cent  lead 
charge  has  been  successfully  smelted,  but  for  good  work,  on 
fairly  high-grade  bullion,  10  per  cent  may  be  considered  as  the 
limit.  A  charge  of  over  12  per  cent  is  rarely  permissible  in  the 
Western  smelting  centres  on  account  of  the  scarcity  of  lead  and 
its  high  cost  as  a  flux.  The  grade  of  the  bullion  must  be  taken 
into  account,  as,  for  example,  some  refiners  will  not  pay  for  gold; 
in  the  bullion  if  it  is  less  than  I  ounce  per  ton,  and  gold  ores 


340  A    MANUAL    OF  PRACTICAL   ASSAYING, 

are  frequently  scarce.  The  smelters  generally  pay  for  95  per 
cent  of  all  the  gold  in  ores  which  assay  over  o.  I  ounce  per  ton.. 
Also,  on  account  of  freight  rates  and  refining  charges  many 
smelters  are  required  to  keep  the  silver  contents  of  the  bullion 
within  rather  narrow  limits,  as,  for  example,  not  below  250  nor 
above  300  ounces  per  ton.  Account  must  also  be  taken  of  the 
silver  and  lead  losses  in  smelting,  the  amount  of  silver  and  lead 
which  goes  into  the  matte,  and  the  amount  of  silver  and  lead 
which  goes  into  the  flue-dust,  in  determining  the  amount  of 
bullion  which  should  be  produced.  No  exact  rule  can  be  given 
for  determining  these  points,  as  they  will  differ  according  to  the 
individual  practice  of  the  works,  and  can  only  be  settled  by  the 
actual  results  at  any  particular  works. 

Fourth.  In  addition  to  the  slag  and  bullion-making  ele- 
ments present  in  the  charge,  we  have  such  elements  as  sulphur 
and  arsenic,  part  of  which  elements  go  to  make  matte  and 
speisse  (a  small  amount  also  passing  into  the  bullion),  and  part 
are  volatilized  in  the  furnace.  The  composition  of  pure  iron 
matte  is  FeS,  but  as  the  furnace-matte  invariably  contains  Cu, 
Ag,  Pb,  Zn,  and  other  constituents  of  the  charge,  its  composi- 
tion is  variable.  The  composition  of  speisse  varies  from  Fe5As 
to  Fe7As  when  pure ;  but  it  almost  always  contains  Cu,  Co,  Ni, 
etc.  Hence  no  exact  rule  can  be  given  for  the  allowance  of 
iron  to  be  made  for  the  sulphur  and  arsenic  on  the  charge. 
Just  what  the  composition  of  the  matte  and  speisse  will  be,  and 
what  the  loss  of  sulphur  and  arsenic  will  be,  will  depend  on  the 
character  of  the  ores  under  treatment  and  the  working  of  the 
furnace.  These  points  can  only  be  determined  by  actual  prac- 
tice in  each  individual  case.  A  rule  which  answers  very  well 
(until  a  more  reliable  one  can  be  formed  based  upon  the  actual 
results  from  the  working  of  the  furnace)  is  to  allow  sufficient 
iron  to  convert  one  half  of  the  sulphur  on  the  charge  into  FeS. 
For  arsenic  allow  sufficient  iron  to  convert  all  the  arsenic  on 
the  charge  into  FeBAs.  As  the  smelting  of  sulphide  and 
arsenical  ores  is  now  usually  preceded  by  roasting,  the  amount 
of  S  or  As  on  the  charge  will  not  be  very  large. 

In  the  case  of  ores  containing  copper,  which  is  almost  always 


CALCULATION  OF  LEAD   BLAST-FURNACE   CHARGES.     34! 

present,  the  charge  must  contain  sufficient  sulphur  to  convert 
all  of  the  copper  into  matte,  as  otherwise  there  will  be  trouble 
with  the  lead-well  and  hearth  of  the  furnace. 

Fifth.  The  size  of  the  charge  and  the  amount  of  fuel  must 
be  taken  into  consideration.  The  size  of  the  charge  will  de- 
pend, to  a  great  extent,  upon  the  size  of  the  furnace.  A  usual 
charge  is  from  700  to  1000  pounds — the  latter  being  a  very 
convenient  ore-and-flux  charge  for  a  modern,  large-sized  blast- 
furnace. In  making  up  a  charge,  the  total  weight  will  fre- 
quently run  under  or  over  the  weight  which  is  desirable,  but 
as  the  question  is  simply  one  of  proportion  the  desired  total 
weight  can  be  obtained  by  increasing  or  reducing  the  weight 
of  each  ore,  the  limestone,  etc*,  by  o.i,  0.2,  or  whatever  pro- 
portion will  give  the  desired  weight.  The  weight  of  fuel  to  be 
used  will  depend  upon  the  character  of  the  charge,  the  fusibil- 
ity of  the  slagj  the  altitude  of  the  place  at  which  the  smelter  is 
situated,  the  character  of  the  coke  and  charcoal,  and  the  di- 
mensions of  the  furnace.  The  fuel  is  usually  spoken  of  as  such 
a  per  cent  of  fuel,  which  per  cent  may  vary  from  12  to  24. 
This  per  cent  is  such  a  per  cent  of  the  total  weight  of  the  ore 
and  flux  exclusive  of  whatever  slag,  from  previous  operations, 
may  be  on  the  charge,  unless  the  amount  of  slag  is  large,  when 
some  fuel  must  be  allowed  for  it.  The  amount  of  sulphur  on 
the  charge  will  affect  the  fuel-charge,  as  some  of  the  sulphur 
will  act  as  a  fuel.  The  amount  of  lead  will  also  affect  the 
amount  of  fuel  necessary,  as  high  lead-charges  will  require  con- 
siderably less  fuel  than  low  lead-charges.  As  an  example  of 
the  effect  of  altitude,  at  Leadville  (10,000  feet  above  sea-levelj 
from  20  to  22  per  cent  of  fuel  is  necessary,  whilst  at  Denver 
(5000  feet  above  sea-level)  15  to  17  per  cent  is  the  usual  charge, 
the  ores  and  fuels  in  both  cases  being  practically  the  same. 
The  character  of  the  fuel  will  make  a  considerable  difference, 
as,  if  the  coke  is  poor  and  friable,  there  will  be  considerable 
waste  in  handling,  and  in  the  furnace,  for  which  allowance  must 
be  made,  The  amount  of  ash  which  the  fuel  contains  and  its 
composition  will  also  have  to  be  taken  into  consideration.  In 
the  winter,  when  the  coke  is  apt  to  be  damp  from  snow  and 


342  A   MANUAL    OF  PRACTICAL   ASSAYING. 

rain,  allowance  must  be  made  for  the  moisture  by  allowing  an 
increased  weight  of  coke. 

The  above  percentages  of  fuel  are  based  upon  a  good,  hard, 
dry  coke,  containing  about  10  per  cent  of  ash,  which  contains 
from  55  to  65  per  cent  of  silica.  High  lime-slags,  and  especially 
those  which  contain  much  baryta,  will  require  a  slight  increase 
in  the  per  cent  of  fuel. 

From  the  above  it  will  be  seen  that  to  calculate  a  charge 
the  first  step  is  to  assume  the  different  ores  and  their  amounts 
which  we  will  have  on  the  charge,  due  consideration  being  given 
to  the  above  points  when  making  this  assumption.  The  second 
step  is  to  find  the  total  amounts  of  silica,  ferrous  oxide,  lime, 
etc.,  in  the  weights  of  ore  as  assumed,  which  is  accomplished  by 
multiplying  the  weight  of  each  ore  by  its  per  cent  of  silica, 
ferrous  oxide,  etc.,  and  taking  the  sum  of  the  different  weights  ; 
a  convenient  way  being  to  tabulate  the  results  as  illustrated  in 
the  examples. 

If  we  assume  the  following  notations  for  the  totals  and  per- 
centages :  A  =  pounds  of  SiO,  in  the  ores  (total)  ;  B  =  pounds 
of  FeO  in  the  ores  (total)  ;  C  =  pounds  of  CaO  in  the  ores 
(total);  */=per  cent  of  SiO2  which  the  iron  ore  (iron-flux  to 
be  added)  contains  ;  e  =  per  cent  of  SiO2  which  the  limestone 
(lime-flux  to  be  added)  contains  ;  /  —  per  cent  of  FeO  in  the 
iron  ore;  /=  per  cent  of  CaO  in  the  limestone  ;  X  =  pounds 
of  iron-ore  required,  and  Y=  pounds  of  limestone  required, 
we  have  for  slag  A 


or 


...      (i) 

and 

C+Yl= 


CALCULATION  OF  LEAD  BLAST-FURNACE    CHARGES.     343 

Solving  equation  (2)  with  respect  to  F,  we  have 


Substituting  this  value  of  Y  in  equation  (i),  we  have 


Reducing  and  transposing,  we  have 


Solving  with  respect  to  X,  we  have 


tfl-Vf-4dl 

For  slag  B  we  have 

(i) 


Solving  equation  (2),  with  respect  to  F,  we  have 

\2B-\-  \2Xf-  I7C 
\r  __      _J  _  -L  _  L__ 


Substituting  this  value  for  F  in  equation  (i),  reducing  and 
solving,  we  have 


-  \jCe-\iBl 
\7fl-i2ef-i7dl  •    •    • 


344  A    MANUAL   OF  PRACTICAL  ASSAYING. 

In  like  manner  we  obtain  for  slag  C 

_  2Al+Be  -  2BI  —  2Ce 
X^  2fl-ef-2dl        '    '     * 


and  in  like  manner  for  slag  D, 

4Al+2r  .    . 


and  in  like  manner  for  slag  E, 


(E') 


and  in  like  manner  for  slag  F, 
_ 


(F') 


In  like  manner  general  equations  may  be  deduced  for  any 
type  of  slag  which  it  is  desired  to  make. 

Having  obtained  the  above  formulae  it  is  only  necessary  to 
substitute  for  A,  B,  C,  d,  etc.,  their  proper  equivalents  in  the 
first  formula  to  obtain  X.  Having  obtained  X,  substitute  its 
value,  together  with  the  proper  equivalents  of  B,f,  C,  and  /,  in 
the  second  formula  to  obtain  Y. 

The  calculation  of  a  charge  is  best  illustrated  by  the  follow- 
ing examples  : 


CALCULATION  OF  LEAD  BLAST-FURNACE   CHARGES.     345 


EXAMPLE  No.  I.  We  have  50  tons  per  day  of  fused  ore,  80 
tons  per  day  of  roasted  ore  and  matte,  a  bed  of  2000  tons  of  ore 
which  it  is  desirable  to  smelt  in  about  two  weeks,  and  a  supply 
of  silicious  silver  ore  which  it  is  desirable  to  smelt  as  rapidly  as 
possible.  In  addition  we  have  a  regular  supply  of  iron  ore, 
limestone,  and  coke.  The  analyses  of  the  ores  are  as  follows  : 


Per  Ct. 
SiOa. 

Per  Ct. 
FeO. 

Per  Ct. 
CaO. 

Per  Ct. 
A1203. 

Per  Ct. 
Zn. 

Per  Ct. 
Cu. 

Per  Ct. 
Pb. 

Per  Ct. 
S. 

Oz. 
per  T. 
Ag. 

Oz. 

perT. 
Au. 

Fused  .  .  . 

30 
10 
28 
90 
10 

5 
5 

30 
30 
21 

6 

75 

4 

4 

8 
8 
5 

"o' 

15 
2O 
21 

3 

5 

2 

50.0 
52-5 
55-o 

1.  00 
0.50 
0.30 

Roasted.  .  . 
Bed 

Silver  
Iron  Ore.. 
Limestone 
Coke*  

50 
2 

3 

*  Ash  =  10  per  cent. 

Suppose  we  assume  that  we  will  smelt  the  ores  in  the  same 
proportions  as  we  have  them  on  hand  and  smelt  50  pounds  of 
silicious  silver  ore  per  charge,  and  use  150  pounds  of  coke  for 
a  1000  charge.  A  convenient  method  is  to  tabulate  the  results 
as  follows  : 


Ore. 

Lbs.per 
Charge. 

Lbs. 
SiOa. 

Lbs. 
FeO. 

Lbs. 
CaO. 

Lbs. 

A1203 

Lbs. 
Zn. 

Lbs. 
Cu. 

Lbs. 
Pb. 

Lbs 
S. 

Oz. 

Ag. 

Oz. 
Au. 

Fused    .... 

IOO 

•3Q 

qo 

8 

1C 

a 

2.  <?O 

O  O5 

Roasted 

1  60 

16 

48 

12    8 

o  6 

32 

8 

4    2O 

o  04 

Bed  

^oo 

84 

63 

12 

12 

15 

63 

6 

8.25 

0.045 

Silver 

qo 

AC. 

a 

2.  =10 

Coke  .  .  . 

mo 

7.  5 

•3 

4.  5 

Total  

760 

182.5 

144 

15 

I6.5 

35-8 

9.6 

no 

17 

17-45 

0.135 

Calculating  one  half  of  the  sulphur  to  Cu,S  and  FeS,  we 
have:  126.8  (mol.  wt.  of  2Cu)  :  158.8  (mol.  wt.  of  CuaS)  1:9.6 
(Ibs.  Cu)  :  x  (Ibs.  of  Cu,S) ;  x  =  12. 

Hence  12  —  9.6  =  2.4  Ibs.  of  S  which  the  Cu  present  will 
take  up.  Now  -y-  —  2.4  =  6.1  Ibs.  S  to  be  taken  up  by  Fe. 

Hence  32  (at.  wt.  S)  :  88  (mol.  wt.  FeS) : :  6.1  :  x  (Ibs.  of  FeS 


34-6  A   MANUAL   OF  PRACTICAL  ASSAYING. 

which  will  be  produced  by  excess  of  S);  x  =  16.7.  Hence 
I6>7  _  6.!  =  10.6  Ibs.  of  Fe  necessary  to  take  up  excess  of  S. 
The  following  gives  the  amount  of  FeO  to  be  deducted  from 
the  total  pounds  of  FeO  on  the  charge  on  account  of  sulphur, 
10.6  XT—  x3-6>  anc*  144-°—  J3-6  =  130.4,  Ibs.  of  FeO  avail- 
able. 

From  an  inspection  of  the  above  totals  slag  "  C  "  appears  to 
be  an  economical  and  good  slag  to  make.  Substituting  in 
equations  (C)  and  (C)  we  have 

(2  X  182.5  X  .5)  +  (*3Q.4  X  .05)  -  (2  X  130.4  X  .5)  -  (2  X  15  X  .05) 
(2  X  .75  X  .5)  -  (-75  X  .05)  -  (2  X  .1  X  .5) 

Y=  130.4 +  (93-2  X  -75)-(2X  15)  = 
2  X  -5 

As  some  of  the  zinc  is  volatilized,  some  passes  into  the 
bullion  and  matte,  and  some  goes  into  the  wall  accretions  of  the 
furnace,  it  is  necessary  to  assume  what  amount  will  pass  into 
the  slag.  If  we  assume  that  80  per  cent  of  the  zinc  passes  into 
the  slag  as  ZnO,  we  will  have  35.6  pounds  of  zinc  oxide  avail- 
able as  slag-making  material.  In  order  to  calculate  the  per- 
centage composition  of  the  slag,  which  will  result  from  the 
above  charge,  it  will  be  necessary  to  calculate  the  pounds  of 
SiO2 ,  FeO,  CaO,  etc.,  in  the  weights  of  iron  ore  and  limestone 
on  the  charge  as  determined  above,  and  add  these  weights  to 
the  above  weights  of  available  SiO2 ,  FeO,  CaO,  ZnO,  and 
A13O3  to  obtain  the  total  weight  of  slag-making  material  on  the 
charge.  Making  this  calculation,  we  have  200.3  (pounds 
SiO3)  +  200.3  (pounds  FeO)  + 100 (pounds  CaO)  +35.6  (pounds 
ZnO)  +  16.5  (pounds  A12O3)  =  552.7.  As  these  elements  will 
not  make  up  the  total  composition  of  the  slag,  it  always  carry- 
ing S,  Pb,  etc.,  it  will  be  necessary  to  assume  what  proportion 
of  the  slag  it  will  make  up.  If  we  assume  -that  these  elements 
will  make  97  per  cent  (an  assumption  which  will  usually  be  very 
near  the  actual  results)  we  will  have 


CALCULATION  OF  LEAD  BLAST-FURNACE   CHARGES.     347 

97  =  35,7percent> 


100  X  97 
CaO  =  V    =  17.55  per  cent, 


ZnO  =  =  6.24  per  cent, 


ALA  =  =  2'89  Per  cent, 


which  shows  the  calculation  to  be  nearly  correct  for  the  type 
of  slag  chosen.  The  amount  of  lead  on  the  charge  is  usually 
spoken  of  as  so  many  per  cent,  referring  to  the  total  ore  and 
flux  charge.  The  following  is  the  calculation  of  the  lead  on 
the  above  charge  : 

no  (pounds  of  lead}  X  100 

—  T-      ;     r  -  —j-ff  —  \  =  12.6  per  cent. 
873.5  (pounds  of  ore  and  flux) 

In  order  to  arrive  at  the  amount  of  bullion  and  matte  which 
should  be  produced  and  its  assay  value,  it  would  be  necessary 
to  assume  the  following  : 

First.  The  amount  of  the  charge  which  will  pass  into  the 
flue-dust.  This  will  depend  upon  the  amount  of  fine  material 
on  the  charge,  the  pressure  of  the  blast,  the  height  of  the 
furnace,  and  the  condition  and  working  of  the  furnace. 

Second.  The  losses  in  lead,  silver,  and  gold  in  smelting  (by 
volatilization  and  in  the  slag).  These  will  depend  upon  the 
character  of  the  ores  and  composition  of  the  slag  and  the  work- 
ing of  the  furnace. 

Third.  The  amount  of  lead,  silver,  and  gold  which  will  pass 
into  the  matte.  These  will  depend  upon  the  character  of  the 
slag,  the  per  cent  and  character  of  the  fuel,  and  the  working  of 
the  furnace. 

All  of  these  are  variable,  and  will  not  only  vary  at  different 
works,  but  will  vary  from  time  to  time  at  any  works,  owing  to> 
the  changes  in  the  ores,  the  working  of  the  furnaces,  etc. 


34-8  A    MANUAL   OF  PRACTICAL   ASSAYING. 

After  a  works  has  been  in  operation  some  time,  reasonably 
close  constants  may  be  deduced  for  these  variables  from  the 
actual  results  obtained  in  smelting. 

In  the  above  example,  suppose  we  assume  that  2  per  cent 
of  the  charge  will  pass  into  the  flue-dust ;  that  the  silver  loss 
in  smelting  is  3  per  cent ;  that  the  lead  loss  in  smelting  is  8  per 
cent ;  that  the  gold  loss  in  smelting  is  nothing  (it  is  usually 
unnecessary  to  make  any  allowance  for  loss  in  gold,  as  a  works 
will  usually  produce  more  gold  than  is  purchased,  owing  to  the 
fact  that  many  of  the  ores  contain  small  quantities  of  gold 
which  are  not  taken  into  account,  and  other  causes) ;  that  the 
matte  will  carry  about  10  per  cent  of  lead,  and  that  the  lead 
passing  into  the  matte  will  carry  with  it  the  same  proportion 
of  silver  and  gold  as  the  lead  in  the  bullion  contains.  Then, 
if  the  Cu2S,  FeS,  and  Pb  make  up  90  per  cent  of  the  matte, 
we  will  have 

110  —  9  (loss  in  smelting)  =  101  pounds  of  lead. 

101  —  2  (amount  passing  into  the  flue-dust)  =  99  pounds  of 
lead. 

17.45  —  0.5235  (loss  in  smelting)  =  16.9265  ounces  of  silver. 

16.9265  —  0.3385  (amount  passing  into  the  flue-dust)  = 
16.588  ounces  of  silver;  and  0.135  —  0.0027=0.1323  ounces 
of  gold  available  for  matte  and  bullion. 

The  composition  of  the  matte  will  be  Cu2S,  12  pounds  ;  FeS, 
16.7  pounds;  Pb,  3.6  pounds.  Balance  (10  per  cent),  3.6 
pounds.  Total  =  35.9  pounds. 

16.588  X  3-6 

— - —     -  =  0.6032  ounce  Ag  m  matte ; 

0.1323  X  3.6 

-  =  0.00481  ounce  Au  in  matte. 

The  assay  value  of  the  matte  in  ounces  per  ton  of  2000 
pounds  will  be 

0.6032x2000  0.00481X2000 

-TT- =33-6  oz.  Ag,  and  -  -=0.27  oz.  Au. 

jj*y  35-9 


CALCULATION   OF  LEAD   BLAST-FURNACE   CHARGES.     349 

The  following  calculation  gives  the  amount  of  bullion  which 
should  be  produced  and  its  assay  value  : 

16.588  —  0.6032    =  15.9848  ounces  Ag  in  bullion, 
and 

0.1323  —  0.00481  =  0.12749  ounces  Au  in  bullion. 


(99  o  -  3.6)  +      -  '        =  ^  ^  ^  of 

which  should  be  produced.     The  assay  value  in  ounces  per  ton 
of  2000  pounds  will  be 

15.9848  X  2000 

-  =  331.202.  Ag, 


96.51 
and 

0.12749  X  2000 
96-51 


=  2.64  oz.  Au. 


The  total  pounds  of  ore  and  flux  on  the  charge  is  873.5.  If 
we  desire  a  looo-pound  charge,  this  weight  is  too  small  by 
about  15  per  cent.  Increasing  the  weight  of  each  ore,  the  iron 
ore  and  limestone  by  15  per  cent,  we  have,  for  the  charge,  fused 
ore,  115  pounds;  roasted  ore,  184  pounds;  bed,  345  pounds; 
silver-ore,  62.5  pounds;  iron  ore,  107.2  pounds,  and  limestone, 
194.9  pounds. 

As  it  is  usual  to  set  the  furnace  scales  only  to  every  5 
pounds  difference  in  weight,  the  charge  would  be — 

Pounds. 

Fused  ore, 115 

Roasted  ore, 185 

Bed, 345 

Silver  ore, 65 

Iron  ore, no 

Limestone, 195 

1015 
Coke  (15  per  cent  of  1015),   ...     150 


350 


A   MANUAL   OF  PRACTICAL  ASSAYING. 


As  the  analyses  are  made  on  the  dry  ore,  allowance  must 
be  made  in  making  up  the  charge  for  the  moisture  which  the 
ores  contain.  In  the  above  example  the  only  ores  liable  to 
contain  sufficient  moisture  to  require  allowance  for  it  are  the 
bed  and  the  iron  ore.  Allowance  would  be  made  in  the  case 
of  these  two  ores  by  adding  such  a  number  of  pounds  as  the 
moisture  determinations,  made  from  time  to  time,  show  to  be 


necessary. 

EXAMPLE  No.  2. 


Suppose  we  have  the  following  ores : 


Ore. 

Tonson 
Hand. 

Pr.  Ct. 
SiOa. 

Pr.  Ct. 
FeO. 

Pr.Ct. 
CaO. 

Pr.Ct. 
A120S 

Pr.Ct. 
ZnO. 

Pr.  Ct. 
Pb. 

Pr.  Ct. 

S. 

Pr.  Ct. 
Cu. 

Oz. 

per  T. 
Ag. 

Oz. 

per  T. 
Au. 

A  

600 

25.0 

20.9 

5.0 

5.O 

6.0 

2O.  O 

3-° 

3O.O 

O.OJ 

B 

2OO 

QO   O 

7   Q 

IOO   O 

o  50 

c  

2OO 

I5.O 

3O.O 

3-O 

IO.O 

I5.O 

6.0 

5-O 

20.  o 

O.5O 

D 

regular 

2O.  O 

At(     O 

iq   o 

8  o 

Limestone.. 

supply 

5-O 

5O.O 

.Iron  ore 

« 

5.O 

80  o 

Coke  

«« 

6.0 

If  we  smelt  the  ores  in  the  proportions  in  which  we  have 
them  on  hand  and  use  ore  D  for  iron-flux,  we  have 


Ore. 

Lbs  per 
Charge. 

Lbs. 
Si03. 

Lbs. 
FeO. 

Lbs. 
CaO. 

Lbs. 
Al,,08 

Lbs. 
ZnO. 

Lbs. 
S. 

Lbs. 
Cu. 

Lbs. 
Pb. 

Oz. 

Ag. 

Oz. 
Au. 

A  
B.... 
C.... 

Coke.. 

3OO 
IOO 
IOO 
150 

75 
90 

15 
9 

62.7 
7-9 
30.0 

15 

15 

18 

9 

60 

4.50 
5-00 
I  .OO 

0.00750 
O.O25OO 
0.02500 

3 
6 

10 

6 

5 

15 

Total 

189 

100.6 

15 

24 

28 

15 

5 

75 

10.5 

0.05750 

Calculating  one  half  the  sulphur  to  Cu,S  and  FeS,  we  have 
86.2  pounds  available  FeO.  Assuming  that  80  per  cent  of  the 
ZnO  passes  into  the  slag  and  adding  this  to  the  CaO,  we  have 
for  available  combined  CaO  and  ZnO  37.4  pounds.  Substitut- 
ing in  equations  (B)  and  (B'),  we  have 

_Y_(i7X  189X0. 5)+(i2X86.2Xo.Q5)-(i7X37-4Xoo5)-(i7X86.2X05)_  gQ 
(!7Xo.45Xo.5)-(i2Xo.o5Xo.45)-(i7Xo.2Xo.5) 


y_  (12  X  86.2)  +  (i 2  X  480-7  X  Q.45)  -  d7  X  37-4^  _ 
17X0.5 


352.2. 


CALCULATION  OF  LEAD   BLAST-FURNACE   CHARGES.     351 

From  the  above  we  have  10.8  per  cent  of  lead  on  the 
charge,  and  allowing  for  a  lo-per-cent  lead  loss  and  a  4-per- 
cent silver  loss  in  smelting,  the  bullion  should  assay  about 
182.7  ounces  of  silver  and  0.88  ounce  of  gold  per  ton  of  2000 
pounds. 

Taking  the  sum  of  the  pounds  of  ore  and  limestone  on  the 
charge,  we  have  a  total  of  1333  pounds,  which  is  about  25  per 
cent  too  much  if  we  wish  a  looo-pound  charge. 

Reducing  the  weights  by  25  per  cent,  we  have,  for  the 
corrected  charge, 

Pounds. 

Ore  A, 225 

Ore  B, 75 

OreC, 75 

Ore  D, 360 

Limestone, 265 


1000 
Coke, 150 

EXAMPLE  No.  3.  Suppose  we  have  assumed  the  number  of 
pounds  of  several  ores  which  we  will  smelt  on  a  charge,  and 
have  figured  out  the  total  pounds  of  SiO2 ,  FeO,  etc.  The 
totals  are  as  follows : 

Lbs.      Lbs.        Lbs.        Lbs.       Lbs.       Lbs.      Lbs.     Lbs.  Oz.  Oz. 

SiO2.     FeO.       CaO.     A12O3.    ZnO.     Cu.        Pb.         S.  Ag.  Au. 

211        177        54.5       30.5        12.       7.5       III       17.5       19.25      0.1075 

Assuming  that  one  half  of  the  S  passes  into  the  matte  as 
FeS  and  Cu2S,  we  have  161.3  pounds  of  FeO  available  for  slag. 
We  have,  for  fluxing,  iron  ore  containing  SiO2  5  per  cent,  FeO 
80  per  cent;  and  limestone  containing  SiO2  5  per  cent,  and 
CaO  50  per  cent.  Slags  A,  B,  or  D  are  all  good  slags  for  the 
above  charge.  If  we  prefer  to  run  slag  A,  we  have  by  substi- 
tution in  equations  (A)  and  (A') 

x      (4X2iiXo.5)4-(4Xi6i.3Xo.Q5)-(4X54.5Xo.05)-(5Xi6i.3Xo.5)  _ 
(5X0.8X0. 5)-(4Xo.o5Xo.8)-(4Xo.05Xo.  5) 

Y  =  l6l-3+(*7.5X  Q.8) -54.5  =         6 
0.5 


352  A   MANUAL   OF  PRACTICAL   ASSAYING. 

Hence  we  would  require  17.5  pounds  of  iron  ore  and  241.6 
pounds  of  limestone  to  flux  the  charge. 

EXAMPLE  No.  4.  We  have  on  a  charge,  before  fluxing,  a 
total  of  available  pounds  as  follows:  SiO'2  200,  FeO  160,  and 
CaO  40. 

Iron  ore  containing  SiO2  5  per  cent  and  FeO  75  per  cent 
costs  $6  per  ton.  Limestone  containing  SiOa  5  per  cent  and 
CaO  50  per  cent  costs  $1.50  per  ton.  It  requires  15  per  cent 
of  coke  to  smelt  the  charge,  and  the  coke  costs  $10  per  ton 
of  2000  Ibs. 

What  type  of  slag  would  be  the  most  economical  ? 

Substituting  in  equations  (A),  (A'),  (B),  (B'),  and  (D),  (D')> 
we  obtain  the  following : 

Slag  A  will  require  15  pounds  of  iron  ore  and  260  pounds 
of  limestone.  Hence  the  flux  will  cost  $0.235  per  charge,  and 
the  fuel  necessary  to  smelt  the  flux  will  cost  $0.206.  Total 
cost,  $0.44. 

Slag  B  will  require  75  pounds  of  iron  ore  and  260  pounds 
of  limestone.  Hence  the  flux  will  cost  $0.3862  per  charge,  and 
the  fue1  necessary  to  smelt  the  flux  will  cost  $0.225.  Total 
cost  $0.6 1. 

Slag  D  will  require  175  pounds  of  iron  ore  and  52  pounds 
of  limestone.  Hence  the  cost  of  flux  will  be  $0.559  Per  charge, 
and  the  fuel  necessary  to  smelt  the  flux  will  cost  $0.1688.  Total 
cost,  $0.73. 

With  labor  and  general  expense  at  $1.25  per  charge,  slag 
B  would  have  to  drive  13  per  cent  faster  than  slag  A,  and  slag 
D  would  have  to  drive  9.6  per  cent  faster  than  slag  B,  and  23 
per  cent  faster  than  slag  A  to  be  as  economical,  other  condi- 
tions being  equal. 


TABLES. 


TABLE  I. 

WEIGHTS   AND    MEASURES. 
MEASURES  OF  CAPACITY. 


Gals.         Qts.         Pts.          FJ.  Oz.          Fl. 

Dr. 

Grains  of  Water               Cubic 
at  62°  F.               Centimetres. 

I      =     4     =      8     =      128     =      I, 

024 

=      58,318.00 

=    3,785.200 

1      =     2     =       32     = 

256 

=      14,579.50 

=       946.  300 

I     =       16     = 

128 

=        7,289.75 

=      473.150 

I      = 

8 

=            455.61 

=        29.570 

I 

=              56.95 

=         3.690 

I 

English  imperial  gallon  =  277.274  cu 

.  in. 

=      7O,OOO.OO 

=    4,543.000 

I 

"       wine   or   Win- 

chester gal.       =  231.000 

it 

=      58,318.00 

=    3,785.200 

I 

"      corn  gallon         =  268.000 

" 

=      67,861.00 

=    4,402.900 

I 

"       ale        "              =  282.000 

" 

=      71,193.40 

=     4,619.200 

I                     CU.  ft. 

= 

283.15  cc. 

i               cu.  in. 

— 

16.38  " 

0.061027       " 

= 

I  " 

LINEAR  MEASURES." 

I  yd.     =     3  ft.     =     36  in.  =  0.91438  metre. 

i  ft.     =     12  in.  =  0.30480       "  T* 

i  in.  =  0.02540       " 

39.3708  in.  =  i.ooooo       " 

TROY  WEIGHT. 
lib.     =     12  oz.     =     240  dwt.     =     5.76ogrs.     =     373.2419  grammes. 

I  "    =    20  "    =    480   "    =    31.1035      " 

I   "     =      24   "    =     1.5552 

I   "    =     0.0648     " 

AVOIRDUPOIS  WEIGHT, 

i  gross  ton     =     20  cwt.     =     2,240  Ibs.     =     i, 016.00  kilogrammes, 
i    "        =        112   "       =          50.80 

Oz.  Grs.  Troy.  Grammes, 

i  lb.     =     16     =     7,000.00     —     453.5926 

I    =      437.50    =     28.3495 

i  net  ton     =     2,000  Ibs.       =  907  kilogrammes, 

i  cu.  ft.  of  water  at  62°  F.     =    62.3550  Ibs.  Av.     =     28,315.0000  grammes, 
i  cu.  in.  "       "      "       "         =      0.0361     "      "        =  16.3862         " 

APOTHECARIES  WEIGHT. 

i  lb.   =  12  oz.  =  96  dr.   =  288  scruples  =  5, 760  grains  =  373.2419  grammes, 
i  (|)  =     8(3)          24  480  31.1035 

i(3)  3  60  3.8879 

I  O)  20  1.2960 

0.0022  lb.  Av.  =  0.03527  oz.  Av.  =  15.4328  =   i.oooo    " 

353 


354 


A   MANUAL    OF  PRACTICAL   ASSAYING. 


TABLE  II. 

ATOMIC   WEIGHTS. 


Name. 

Sym- 
bol. 

Quantiv- 
alence. 

Atomic 
Weight. 

Name. 

Sym- 
bol. 

Quantiv- 
alence. 

Atomic 
Weight 

Aluminium 

Al 

IV 

27.0 

Hg 

II 

2OO  O 

Antimony 

Sb 

V 

I2O.O 

Molybdenum.  . 

Mo 

VI 

06  o 

As 

v 

74.  Q 

Nickel  

Ni 

VI 

Barium 

Ba 

II 

136.8 

N 

v 

14  O 

Bi 

V 

2IO.O 

Osmium  

Os 

IV 

IQQ  O 

Boron        .   .  .  . 

B 

III 

II.  O 

Oxygen  

o 

II 

16  o 

Bromine  

Br 

I 

8O.O 

Pd 

IV 

1  06  o 

Cd 

II 

112.  0 

Phosphorus.  .  . 

P 

v 

•31  o 

Caesium           . 

Cs 

I 

IT?.  O 

Platinum  

Pt 

IV 

IO7  O 

Calcium  

Ca 

II 

4O.O 

Potassium  .... 

K 

I 

-2Q     T 

Carbon        . 

c 

IV 

12.  0 

Rhodium 

Ro 

IV 

Cerium  

Ce 

III 

.      I4I.2 

Rubidium.  .  .  . 

Rb 

I 

8s  o 

Chlorine   ..... 

Cl 

I 

35.5 

Ruthenium.  .  .  . 

Ru 

IV 

104  o 

Chromium  .... 
Cobalt     .  .      . 

Cr 
Co 

VI 
VI 

52.4 

CQ.O 

Selenium  
Silicon  .... 

Se 

Si 

II 

IV 

79.0 
28  o 

Columbium  .  . 

Cb 

V 

04.0 

'Silver  

Ae- 

I 

108  o 

Cu 

II 

63.1 

Na 

I 

27  o 

Didymium  .... 

D 

III 

147.  0 

Strontium 

Sr 

II 

87  5 

Erbium  

E 

III 

l6q  O 

Sulphur  

s 

II 

•22  o 

F 

I 

IQ.O 

Tantalum.  .  .  . 

Ta 

v 

182  o 

Gallium  

Ga 

III 

60.  Q 

Tellurium  . 

Te 

II 

128  o 

Glucinum  

Gl 

II 

Q.2 

Thallium 

Tl 

I 

Gold  

Au 

III 

196.2 

Thorium  

Th 

IV 

2-iT   C 

Hydrogen.  .  .  . 

H 

I 

I.O 

Tin  

Sn 

IV 

118  o 

Indium  

In 

III 

11^.4 

Titanium 

Ti 

IV 

CO  O 

Iodine  

I 

I 

126.85 

Tungsten.  .    . 

W 

IV  VI 

184  o 

Iron  .  . 

Fe 

VI 

c6  o 

Uranium 

u 

VI 

Lanthanum.... 
Lead  

La 
Pb 

III 
II 

139.0 
207.0 

Vanadium  .... 

V 
Y 

V 
III 

51.2 

60  o 

Lithium     

Li 

I 

-7  o 

Zinc 

Zn 

II 

Magnesium...  . 
Manganese.  .  .  . 

Mg 
Mn 

II 

VI 

24.0 

55-o 

Zirconium  .... 

Zr 

IV 

90.0 

TABLES. 


355 


TABLE  III. 

TENSION   OF  AQUEOUS  VAPOR  AT  VARIOUS   TEMPERATURES.* 


Temperature 
in  Degrees 

Tension  of  the 
Aqueous  Vapor  in 
Millimetres. 

Temperature 
in  Degrees 

Tension  of  the 
Aqueous  Vapor  in 
Millimetres. 

O 

4.525 

21 

18.505 

I 

4.867 

22 

I9-675 

2 

5-231 

23 

20.909 

3 

5.619 

24 

22.211 

4 

6.032 

25 

23.582 

5 

6.471 

26 

25.026 

6 

6-939 

27 

26.547 

7 

7'436 

28 

28.148 

8 

7.964 

29 

29.832 

9 

8.525 

30 

31  .602 

10 

9.  126 

31 

33-464 

ii 

9-751 

32 

35-4!9 

12 

10.421 

33 

37-473 

13 

11.130 

34 

39.630 

14 

11.882 

35 

41.893 

15 

12.677 

36 

44.268 

16 

13.519 

37 

46.758 

17 

14.409 

38 

49.368 

18 

15.351 

39 

52.103 

19 

16.345 

40 

54-969 

20 

17.396 

*  For  a  more  complete  table  see  Winkler's  "  Technical  Gas  Analysis." 


356  A   MANUAL   OF  PRACTICAL  ASSAYING. 

TABLE  IV. 

DENSITIES  AND   LITRE-WEIGHTS  OF  GASES  AND  VAPORS.* 


Name  of  the  Gas. 

Molecular 
Formula. 

Density. 

1000  cc.  of  the 
Gas  in  the 
Normal  State 
weighs, 
Grammes  — 

C2H2 

12.970 

1.1621 

14.422 

I  2922 

H3N 

8.510 

o  7625 

H3Sb 

62.545 

5.6040 

H3As 

38.060 

3-1008 

'  C6H6 

38.010 

3  4863 

C4H8 

27  Q4O 

2  ^O3J. 

CO 

13  06? 

I  25  12 

CO3 

21.945 

I  0663 

CS2 

•37    Q6C 

3dOI  7 

COS 

2Q   QCC, 

2  6830 

C12 

35.37O 

3  1  60  1 

(CN)a 

25.QQO 

2  3287 

C2H6 

14  O.7O 

I   2.1  1  3 

C2H4 

13  Q7O 

I  2^17 

H3 

I.OOO 

o  0896 

HC1 

18  185 

I  62O1 

HCN 

13  4.Q5 

I   2O9I 

H2S 

l6  QQO 

I    5223 

CH4 

7.085 

O  71  54 

N2 

14  O2O 

I  2562 

N2O 

22  OOO 

I  O71  2 

Nitric  oxide                 <  •    . 

NO 

Nitrogen  trioxide  ••    

N2O3 

37  060 

*•  J4J1 

NO2 

22  Q7O 

2  O58l 

O2 

IE  060 

I  43OO 

H8P 

16  980 

I    H2Izl 

C3H6 

2O  Q55 

I  8775 

SiF4 

C2  055 

4  6641 

Sulphur  dioxide  

SO2 

31  Q^O 

2  8627 

Water  

H2O 

8  980 

o  8046 

*  Taken  from  "Technical  Gas  Analysis,"  by  Winkler  and  Lunge,  London, 
1885. 


TABLES. 

TABLE  V. 

FACTORS. 


357 


Found. 

Required. 

Factor. 

Found. 

Required  . 

Factor. 

A1PO4 

Al 

O  22  131 

Mg2P2O7  .... 

p 

A12O3         

Al 

o  52042 

P2O5 

o  6306^ 

Sb2O4   

Sb 

O.78Q47 

MgO 

o  36036 

Sb2S3  

Sb 

0.71428 

MgO  

McCO3 

2   IOOOO 

Mg2AsQO7 

As 

o  48353 

Mn.-  

MnO 

Ag3AsO4  

As 

o  16181 

Mn3O4.'  

Mn 

i.^yuyi 

o  72052 

CaSO4  

CaO 

0.41176 

Mn2P2O7  

Mn 

o  38732 

CaO     

CaCO3 
CaCO3 

0.73529 

I  78571 

(NH4)3i2Mo03P04 

P 

PoOft 

0.01630 

O  O37T5 

Cr2O3  

Cr 

o  68586 

NiO  

Ni 

o  78667 

CO2   

c 

o  27273 

K2PtCl6  

KC1 

o  30561 

CoSO4  

Co 

0.38065 

K2O 

O  IQ2Q5 

CoO     

Co 

o  78667 

,  NaCl  

Na2O 

O  52OOI 

Cu  

CuO 

I  25356 

SiO2  

Si 

o  46667 

BaSO4  

BaO 

0.65636 

BaSO4  

s 

O  13745 

Fe2O3  

Fe 

0.70000 

SO3 

o  34364. 

Fe  

FeO 

I  28571 

PbSO4  

s 

o  10561 

Fe3O4 

I  "38005 

SnO2  

Sn 

o  78667 

PbSO4  

Pb 

o  68317 

TiO2  

Ti 

O  6OQ75 

PbS  

Pb 

o  86611 

ZnO     .    .      . 

Zn 

o  80247 

d   MANUAL   OF  PRACTICAL  ASSAYING. 

TABLE  VI. 

THE    QUANTITATIVE   PRECIPITATION  OF  VARIOUS  METALS 
BY  ELECTROLYSIS.* 


Solution. 

Au 

Pt 

Pd 

Ag 

Hg 

Pb 

Sb 

Sn 

Cu 

Nitric  or  sulphuric 
Double   ammonium 

- 

- 

- 

- 

+_« 

- 

Double  ammonium 

Double     potassium 

Sulpho-salt             . 

In  glacial  phospho- 
ric   acid,    after 
(NH4)aC03.... 

- 

Solution. 

Bi 

Cd 

Tl 

Al 

Fe 

Mn 

Zn 

Co 

Ni 

Nitric  or  sulphuric 
Double  ammonium 
oxalate  

- 

- 

*' 

•4-d 

•4-eA 

—  e 

Double  ammonium 
sulphate        . 

-\-ci 

Double     potassium 

1     V 

Sulpho-salt     

In  glacial  phospho- 
ric   acid,    after 
(NH4),CO,.... 

- 

- 

- 

+ 

— 

- 

— 

—  .      Precipitated  at  cathode  in  metallic  form. 


after  adding  (NH4)2SO4. 

The    corresponding    potassium 

salt  preferable, 
after     adding  NaaCoHoOi    and 


anode  as  PbO3. 
"  "  T1208. 
"  "  MnOa. 


incompletely.       Completely  from  corre- 
sponding potassium  salt, 
incompletely. 


*  From  an  article  by  Kahn  and  Woodgate  in  J.  S.  Chem.  Ind.,  vol.  viii.  p. 


256. 


TABLES. 


359 


TABLE  VII. 

SOLUBILITY,    FUSIBILITY,    ETC.,   OF  VARIOUS   METALS. 


Metal. 

Color. 

Tenac- 
ity. 

Hard- 
ness. 

Sp.gr. 

Melts 
at 
Deg.  C. 

Best  Solvent. 

Gold  v  .  . 

yellow 

mal. 

2.  5—  "3 

IQ—  2O 

1064 

ao.ua  rec[ia 

Platinum.. 

Silver  .  .  . 

whitish  to  steel-gray 
white 

4-4-5 
2.C.—  q 

1  6-2  1 
IO.5—II 

1808 
062 

«« 
HNOS 

Lead  

bluish 

« 

I.c 

II.  4^ 

322 

HNO3 

Mercury  ... 
Bismuth.  .. 
Copper  
Cadmium  . 
Arsenic.... 
Antimony. 
Tin 

tin-white 
silver-white  to  reddish-wh. 
red 
tin-white 
lead-gray 
bluish-white 
white 

liquid 
brittle 
mal. 

brittle 
« 

mal 

2-3-5 
2-5-3 

I 

4 

3-3-5 

4.—  q 

13.5 
9-7 
8.9 
8.6-8.7 

5-9 
6.8 

7  28 

-40* 
258 
1050 
320 
t 
432 
228 

HN03 
HNO3 
HNO3 
HNO, 

aqua  regia 

HC1 

Iron  (cast). 
Iron  (w't). 
Steel  

gray 

< 

« 

4-5 
4-5 
6-7 

7-1 
7.6-7.8 

7.8-7.Q 

1530 
1808 
1808 

HC1 
HC1 
HC1 

Aluminum 
Nickel..., 
Cobalt  
Manganese 
Zinc.  .  .  . 

silver-white 

steel-gray  to  reddish 
grayish-white 
bluish-white 

< 

« 

brittle 
mal. 

2 

5-6 
5-6 
9-10 

2 

2.5-2.7 
8.2-8.7 
8.5-8.7 

7.1-8 
6.8-7.2 

700 

1537 
1600 
1650 

411 

HC1 
HN03 
HNO3 
HC1 
HC1 

i 

*  Volatilizes  at  360°  C. 


f  Volatilizes  at  356°  C. 


360  A    MANUAL   OF  PRACTICAL  ASSAYING. 

TABLE 
PROPERTIES  OF 


Ele- 
ment 

Object. 

Obtained  by  or 
Precipitated  with— 

Obtained  or 
Precipitated  as  — 

Conditions  of  Solution. 

K 

Weigh- 
ing 

Weigh- 
ing 

Precipitant  PtCl4.      Pre- 
cipitate   preferably  dis- 
solved in  hot  HaO  anc 
evaporated  in  a  weighed 
vessel. 

Precipitant  PtCl4. 

KaPtCl« 
KaPtCl« 

Cold,    alcoholic,  contain- 
ing   chlorides    or    HC1. 
Salts   other   than    NaCl 
should  be  absent.     Small 
amounts  of  Ca  or  Mg  may 
be  present,  but  are  detri- 
mental. 
As  above. 

Weigh- 
ing 

Weigh- 
ing 

Evaporation   and    gentle 
ignition.       Volatile     at 
temperatures     above    a 
dull  red. 

Evaporation      and      igni- 
tion.   (NH4)2CO,  facili- 
tates conversion. 

KC1 

KaS04 

Only    chlorides    or    salts 
converted  into  chlorides 
should  be  present.     Am- 
monium   salts    may    be 
present. 
Absence  of  salts  forming 
non-volatile  sulphates  or 
containing     non-volatile 
acids  (as  H3PO4). 

Na 

Weigh- 
ing 

Evaporation    and   gentle 
ignition. 

NaCl 

Same  as  KC1. 

Weigh- 
ing 

Same  as  K2SO4. 

Na2SO4 

Same  as  KaSO4. 

Ca 

Weigh- 
ing 

Weigh- 
ing 

Precipitant     (NH4)2C2O4 
or  H2C2O4  in   NH4OH 
solution. 
As  above. 

CaC204 
CaC204 

Hot,  strongly  ammoniacal 
and  an  excess  of  oxalate. 

As  above. 

Separa- 
tion 

Precipitant  (NH4)aCO3. 

CaC03 

Alkaline      solution      free 
from     large    excess    of 
alkaline  salts,  especially 
citrates. 

Mg 

Weigh- 
ing 

Separa- 
tion 

Precipitant  NaaHPO4. 
Precipitant  Ba(OH),. 

MgNH4P04 
Mg(OH)a 

Dold,  containing  excess  of 
NH4OH  +  NH4C1.     Ab- 
sence of  SiOj  and  bases 
other  than  alkalies. 
Alkaline   and   moderately 
concentrated.  Free  from 
ammonium  salts  and  or- 
ganic salts. 

Ba 

Weigh- 
ing 

Precipitant              H2SO4. 
Should  be  heated  before 
adding. 

BaSO4 

riot,  containing  some  free 
HC1.     Absence  of  SiO2  , 
large  amounts  of(NH4)2S 
group  and  Ca  salts. 

Separa- 
tion 

Precipitant  (NH4)aCO8. 

BaCO, 

Alkaline,           containing 
NH4OH    and  excess  of 
(Nrf4)2C03. 

*  Compiled  mainly  from  an  article  by  Prof.  E.  Waller,  entitled 


TABLES. 


361 


VIII. 

PRECIPITATES.* 


Soluble  in— 

Contaminants. 

Prepared  for 
Weighing  by  — 

Weighed 
as  — 

Slightly  soluble    in    cold, 
more    so    in    hot,   H2O. 

NaCl   and  other  salts  (as 
sulphates)    insoluble    in 

Drying. 

K2PtCl6 

Solubility  increased    by 
alkali  or  acid,  diminished 

alcohol.      Removed     by 
washing    with      H2O  -j- 

by  PtCl4  or  Na2PtCl6. 

NH4Cl-f  K2PtCl6. 

As  above 

As  above. 

Ignition  gently  at  first. 

Pt 

Addition    of    H2C2O4 

aids  reduction. 

In  water.    Less  in  alcohol 

NaCl,  and  if  long  exposed 

Ignition    not    above  a 

KC1 

or  strong  HC1. 

to  the  air,  organic  dust. 

dull  red. 

Moderately  in  H2O,  much 
less  in  alcohol. 

Na2SO4  or  other  non-vola- 
tile sulphates. 

Ignition    over   an  ordi- 
nary Bunsen  flame. 

K2SO4 

Same  as  KC1. 

KC1    and   other  salts   (as 
sulphates)    insoluble    in 

Ignition    not    above    a 
dull  red. 

NaCl 

alcohol. 

Same  as  KaSO4. 

K2SO4    and    other    non- 

Same as  K2SO4. 

Na2SO4 

volatile  sulphates. 

Mineral    acids.      Slightly 
in  H,,C  04. 

MgC2O4,  which  is  removed 
by   solution  in  HC1  and 

Ignition,  gently  at  first, 
and  finally  over  blast- 

CaO 

reprecipitation. 

lamp. 

As  above. 

As  above. 

Addition      of     H2SO4, 

CaS04 

evaporation,  and   igni- 

tion.    In    presence   of 

C  add  HNO3. 

H2O  containing  CO2.     In 

BaCO3    and    MgCO3,  if 

acids  and  in  hot  solution 

much  are  present. 

of  NH4C1.     Insoluble  in 
H2O+NH4OH  +(NH4)2 
CO3. 

Acids.   Hot  solutions,  and 
slightly    in    cold     H2O. 
Insoluble  in  NH4NO3. 

SiO2  and  Mg(OH)2. 

Ignition,  gently  at  first, 
finally    intensely.     In 
presence    of    C      add 

Mg2P207 

NH4NO9. 

Acids     and     ammonium 

Usually   unimportant  for 

salts.    Prevented  by  or- 

purposes of  separation. 

ganic  salts. 

Cone.  H2SO4,    in    strong 
hot    HC1     and     HNO3 

Alkaline        and        alkali- 
earth      chlorides,     chlo- 

Ignition.     In  the    pres- 
ence of  C  the  addition 

BaSO4 

(dilute).     In  strong   hot 
Fe2Q6  and   in    alkaline 

rates,sulphates,  nitrates, 
basic,  ferric,  or  aluminic 

of  HNOs  is  necessary. 

or  alkali-earth    nitrates. 

compounds.      Repeated 

In  citrates. 

boiling    in     very    dilute 

HC1  assists  in   removal, 

but    liable    to    dissolve 

some  of  the  precipitate. 

H2O  containing  CO2  and 
acids.      In    hot    NH4C1. 

MgCO3  if  much  is  present, 
and    carbonates    of    the 

Insoluble  in   NH4OH-f 

fixed  alkalies. 

(NH4)2C03. 

•*  Properties  of  Precipitates,"  School  of  Mines  Quarterly •,  vol.  XH. 


362 


A   MANUAL   OP   PRACTICAL  ASSAYING. 

PROPERTIES    OF 


Ele- 
ment. 

Object. 

Obtained  by  or 
Precipitated  with— 

Obtained  or 
Precipitated  as  — 

Conditions  of  Solution. 

Fe 

Weigh- 
ing 

Precipitant           NH4OH. 
Addition  of  NH4C1  aids 

Fea(OH)6 

Alkaline,  and    free    from 
H3S. 

precipitation. 

Separa- 

As above. 

Fe2(OH)6 

As  above. 

tion 

Separa- 
tion 

Precipitant       NaCaH3O2. 
Filtered  hot. 

FetOH)n(C2Hs 
02)6-» 

Dilute     containing     but 
little    free       HC2H3O2. 
Hut,  but  too  long  boiling 
should  be  avoided. 

Al 

Weigh- 
ing 

Precipitant                (usual) 
NH4OH.     Best     precip- 
itated   by  adding  slight 
excess  NH4OH.  boiling, 

A12(OH)6 

Neutral  or  slightly  alka- 
line,  containing   prefer- 
ably NH4C1. 

and  passing  H2S. 

Separa- 

Same as  Fe. 

Al2(OH)n(C2H3 

Same  as  Fe. 

tion 

02)6-n2 

No  free  acetic  acid  should 

be  present. 

Cr 

Weigh- 

Precipitant NH4OH.   Ex- 

Cra(OH)6 

Absence    of    members  of 

ing 

cess  removed  by  boiling. 

the   (NH4)2S  group,  and 

preferably  all    non-vt>la- 

tile  salts.     Solution  must 

be  neutral. 

Ti 

Weigh- 
ing 

Insoluble  form  by  boiling 
the     solution      acidified 

H2Ti03 

Dilute     containing      but 
little  free   H2SO4.     HC1 

with  HaS04. 

and    chlorides    must   be 

absent.   HC2H3O2  facil- 

itates precipitation.  Pro- 

Separa- 
tion 

Fusion  and  leaching  until 
filtrate  runs  cloudy. 

(xNa20,  Ti02) 
Na2Ti03 

longed  boiling  also. 
Long  fusion  with  Na2CO» 
at  high  temperature. 

Zn 

Weigh- 

Precipitant NaaCO8. 

2ZnCO3,  Zn(OH)2 

Absence  of  caustic  and  bi- 

ing 

carbonate    alkalies    and 

ammonium  salts. 

Separa- 
tion 

Precipitant  H2S  in  boiling 
dilute    HC2H3O2    solu- 
tion.    NH4C1   facilitates 

ZnS.H2O 

Alkaline  or  acid  only  with 
weak  organic  acid.  Free 
mineral    acids     prevent 

precipitation. 

precipitation         (H2SO4 

least).      Fe     should     be 

absent. 

Mo 

Weigh- 

Precipitant NaNH4HPO4 

MnNH4PO4 

Mn    must  be  entirely  in 

ing 

in    presence  of    ammo- 
nium salts. 

manganous     form,     and 
slightly     alkaline.       An 

excess   of    phosphate    is 

necessary.    Oxalates  and 

excessive     amounts     of 

ammonium  salts   should 

be  absent. 

Separa- 
tion 

Br  from  acetate  solution. 
KC1O8      from      boiling 
nitric-acid  solution. 

MnO2 

Absence  of  HC1  or  other 
halogen     acids.        Also 
lower  oxides  of  nitrogen 

or      reducing        agents. 

Boiling  necessary. 

TABLES. 


PRECIPITATES. 


Soluble  in  — 

Contaminants. 

Prepared  for 
Weighing  by  — 

Weighed 
as  — 

Mineral    acids    and    solu- 
tions   containing    citric, 
tartanc    acids,    etc.,    or 
organic     substances    (as 
sugar). 
As  above. 

In  cold  mineral  acids. 
Also  in  citrates  and  or- 
ganic substances.  Insolu- 
ble in  hot  very  dilute 
HC2H302. 

Basic     ferric     salts,     Cr, 
P2O5  ,  Al,  Mn,  Zn,  Co, 
Ni,  Mg,  SiO  2,  etc. 

As  above. 

Salts    of     fixed    alkalies; 
Si02  ,  P206  ,  Al.  Cr,  Co, 
Ni,    Zn,    Mn,    Cu,    etc. 
Removed    by  resolution 
and  reprecipitation. 

Ignition.  In  presence 
ofC,HNO3  or  NH4NO 
should  be  added.  Vol- 
atile in  presence  oi 
chlorides. 

Fe203 

Acids  and  fixed  alkalies. 
Slightly  in  cold  NH4OH. 

Basic      Al    salts;     SiO2  , 
P2O5,    Al,    Cr,   Co,   Mi, 

Ignition.  Slightly  vola- 
tile in  presence  of 

A1203 

Tartrates,    citrates,    su- 
gar, etc.,  prevent  precip- 
itation. 
Same  as  Fe,  except  slight- 
ly soluble  in  hot    dilute 
HC2H302. 

Zn,  Mn,   etc.     Removed 
by  resolution  and  repre- 
cipitation. 
Same  as  Fe. 

NH4C1. 

All  acids  in  NaOH,  KOH, 
and  slightly  in  NH4OH. 
Tartrates,  citrates,  sugar, 
etc.,  prevent  precipita- 
tion. 

Same  as  Al. 

Ignition. 

Cr20, 

Soluble  form  same  as  Fe2 
(OH)6. 
Insoluble  form   by  fusion 
with  KHSO4  or  boiling 
with     cone.       HC1     or 
H2S04. 
Acids.    Slightly  in  HaO. 

Fe2O3  ,  A12O3  ,  SiO2  ,  and 
P2O5.     Fe2O3and  Al2O3 
removed    by  resolution, 
reduction      with      SO2  , 
and     reprecipitation    in 
presence  of  HC2H3O2 
Fe2O3,    acid-sodium    sili- 
cate, alkali-earth  carbon- 
ates, etc. 

Ignition  with  addition 
of  (NH4)2CO3. 

TiOa 

Dilute  acids,  fixed  caustic 
alkalies,  bicarbonates, 
and  organic  solutions. 

Dilute  HC1  and  HNO3  , 
strong  H2SO4  when  hot. 
Free  NH4OH  retards 
precipitation. 

Alkaline     carbonate     re- 
moved      by        repeated 
washing  with  hot   H2O. 
Fe2O3,  A12O3,  and  SiO2 
removed  by  solution  and 
precipitation  of    the    ig- 
nited ZnO. 
Mn,  Co,  and  Ni  sulphides. 
Removed  by  resolution, 
neutralizing,  and   repre- 
cipitation.     Fe    if     not 
previously  removed. 

Ignition;  absence  of  C 
is  necessary. 

ZnO 

Acids.  Slightly  in  large 
excess  of  ammonium 
salts.  The  influence  of 
ammonium  salts  is 
lessened  by  large  excess 
of  the  precipitant. 

Dilute  mineral  acids  (es- 
pecially HC1).  Insoluble 
in  strong  HC2H3O2  and 
cone.  HNO3. 

None  if  bases  forming  in- 
soluble   phosphates    are 
absent  and  precipitate  is 
well  washed. 

Salts    of    fixed     alkalies, 
Fe2O3  ,  ZnO. 

Ignition.  Gently  at  first. 

Mn2P307 

364 


A   MANUAL   OF  PRACTICAL  ASSAYING. 

PROPERTIES   OF 


Ele- 
ment. 

Object. 

Obtained  by  or 
Precipitated  with— 

Obtained  or 
Precipitated  as— 

Conditions  of  Solution. 

Ni 

Weigh- 
ing 

Electrolysis. 
(See  Table  VI.) 

Ni 

Absence     of     all      other 
metals     of     H2S      and 

(NH4^2S     groups.        Ni 

present  as  oxalate,  sul- 

phate,    or    dcuble    am- 

monium nitrate,  and  ex- 

cess of  NH4OH. 

Weigh- 
ing 

Precipitant       KOH       or 
NaOH. 

Ni(OH)2 

Bases    other     than    fixed 
alkalies  should  be  absent. 

Separa- 
tion 

Precipitant  H2S  in  weak 
HC2HgO2  solution. 

NiS.H02 

Absence  of    other    mem- 
bers    of     the     H2S     or 
(NH4)2S  groups.   NH4C1 

aids  precipitation. 

Co 

Weigh- 
ing 

Precipitant  KNO2  in  solu- 
tion   slightly  acid   with 
HC2H302. 

6KN02)Coa(N02)6 

Warm,     containing    only 
Co,  Ni,  and  K  salts,  and 
nearly    saturated     with 

KC2H3O2. 

Weigh- 

Electrolysis. 

Co 

Same  as  Ni. 

ing 

(See  Table  VI.) 

Separa- 

SameasNiS.H2O. 

CoS,H2O 

Same  as  NiS,H2O. 

tion 

Cu 

Weigh- 
ing 

Electrolysis. 
(See  Table  VI.) 

Cu 

HVSO4   solution    contain- 
ing a  few  drops  of  HNO3 
preferable.  Organic  acids 

should  be  absent. 

Separa- 
tion 

Precipitant  H2S  in  dilute 
acid  solution. 

CuS 

Moderately  strong  HC1  or 
H2SO4.       If     HNOS    is 

present,       the      solution 

must  be  cold  and  dilute. 

Pb 

Weigh- 
ing 

Precipitant  H2SO4. 

PbSO4 

Excess  of  HoSO4  ,  and  but 
little      HNO3    or    HC1. 

NH4  salts    and   salts  of 

organic    acids    must    be 

absent. 

Weigh- 
ing 

Precipitant    K2Cr2O7    in 
acetic-acid  solution. 

PbCrO4 

Bi,  Ag,  Fe,  and  Ba  should 
be     absent.      Chlorides 

should    be    absent,   and 

also    alkaline     citrates, 

tartrates,  etc. 

Separa- 
tion 

Precipitant  HaS. 

PbS 

Slightly  acid,  neutral,  or 
alkaline.     Best    precipi- 

tated   in     cold     H2SO4 

solution. 

Ag 

Weigh- 
ing 

Precipitant   HC1  in  very 
slight  excess. 

AgCl 

Slightly  acid  with    HNO, 
free  from  chlorides. 

Separa- 
tion 

Precipitant  NaBr. 

AgBr 

Same  as  AgCl. 

TABLES. 


365 


PRECIPITATES. 


Soluble  in— 

Contaminants. 

Prepared  for 
Weighing  by- 

Weighed 
as  — 

Readily  in  HNO3.  Slowly 
in  strong  (NH4)2C2O4. 

Mineral    acids.      In    am- 
monium salts,  tartrates, 
citrates,  etc. 
Precipitation      prevented 
by  moderate  amounts  of 
free    acetic    or    mineral 
acids.  Soluble  in  mineral 
acids  and  KCN. 

Co,    Fe,   and   Zn,   unless 
previously  separated. 
(See  Table  VI.) 

Alkalies,  Fe2O3  ,   A12O3  , 
and  SiO2  from  reagents. 

Sulphides    of     H2S    and 
(NH4)2S  groups,  if    not 
previously  removed. 

Drying  at  gentle  heat. 
(See  Cu.) 

Ignition  strongly. 

Ni 
NiO 

~^w 

Co 

H20,  acids  NH4  and   Na 
salts.  Insoluble  in  dilute 
HC2H302  and  alcohol. 

Same  as  Ni. 
Same  as  NiS,H2O. 

Ca  and  Pb  if  present.     K 
salts  should  be  removed 
by  careful  washing. 

Same  as  Ni. 

Ni  and  other  members  of 
(NH4)2S    group,  if     not 
previously  removed    by 
separation. 

Dissolve       in        dilute 
H2SO4  ,  and  evaporate 
in    a  weighed    vessel. 
Ignition. 
Same  as  Ni. 

HN03  and  HC1.    Deposit 
prevented     by    Cl,    too 
strong  acid,  or  lower  ox- 
ides of  nitrogen. 

Hot    dilute     HNO,    and 
strong  hot  HC1. 

As,  Sb,  or  Bi,  if  HNO3  is 
not   present.     If    HNO3 
and  Zn   are   present,  Zn 
will  begin  to  precipitate 
as  soon  as  Cu  is  all  pre- 
cipitated. 
(See  Table  VI.) 
Other    members    of    the 
H2S  group. 

Washing  with  H2O  and 
then      with      alcohol. 
Drying  at  a   tempera- 
ture   which     can      be 
borne  by  the  hand. 

Cu 

Cone,    mineral    acids;    in 
Na2S2O3  ;  in  NH4  salts, 
and    especially  those  of 
organic  acids. 

Moderately    strong    min- 
eral acids;  in  hot  NH4C2 
H3O2.     Insoluble   in  di- 
lute HNO3. 

Dilute  boiling  HNO3  ;  hot 
cone.  HC1.    In  Na2S2O3. 

Other    sulphates,    which 
are  removed  by  washing 
with  very  dilute  H2SO4. 

Ba,    Bi,   Hg,    and     chro- 
mates.      If  much  Fe  is 
present,      possibly    Fe2 
(Cr04)3. 

Other    members    of    the 
H2S  group  if  present. 

Ignition.     If  C  is  pres- 
ent, treat   with   HNO3 
-)-  H2SO4  ,    evaporate, 
and  ignite. 

Drying    on    previously 
weighed  filter. 

PbSO4 
PbCrO* 

Partially    in     strong    hot 
HClorHN03.   Partially 
in  alkaline  and  alkaline- 
earth  chlorides.    Readily 
in   NH4OH,   KCN,   and 
Na2S203. 
Same  as  AgCl. 
Insoluble  in  considerable 
excess  of  precipitant. 

Chlorides  of  Pb  and  Hg 
if  present  in  the  solution. 

Ignition  until  the  edges 
fuse.       Volatile    at    a 
temperature      slightly 
above  dull  red. 

AgCl 

366  A   MANUAL   OF  PRACTICAL  ASSAYING. 

PROPERTIES   OF 


Ele- 
ment. 

Object. 

Obtained  with  or 
Precipitated  by- 

Obtained  or 
Precipitated  as  — 

Condition  of  Solution. 

As 

Weigh- 
ing 

Weigh- 
ing 

Precipitant  HaS  in  HC1 
solution. 

Precipitant  MgCl2  in  am- 
moniacal  solution  con- 
taining alcohol. 

As2S, 
MgNH4AsO4 

Acid  with  mineral  acid 
(preferably  HC1). 

Alkaline  with  NH4OH, 
containing  a  minimum 
of  NH4C1  and  30  per  cent 
of  alcohol. 

Sb 

Weigh- 
ing 

Precipitant  H2S  in  acid 
solution,  or  upon  acidify- 
ing solutions  of  sulph- 
antimonite. 

Sb2S3 

Slightly  acid  and  moder- 
ately dilute. 

So 

Weigh- 
ing 

Precipitant  H2S  in  acid 
solution  or  upon  acidify- 
ing solutions  of  alkaline 
sulpho-stannate. 

SnS2 

Moderately  dilute  and 
slightly  acid.  Precipi- 
tation promoted  by 
acetates  and  interfered 
with  by  oxalates  or  ox- 
alic acid. 

P 

Weigh- 
ing 

Separa- 
tion and 
Titration 

MgCl-j     in     ammoniacal 
solution            containing 
NH4C1. 
Precipitant    (NH4)2MoO4 
in  HNOS  solution  heated 
to     80°    C.       Agitation 
facilitates  precipitation. 

MgNH4PO4 

i2MoOs(NH4)8 
P04  + 

Same  as  Mg. 

Acid  with  HNO3,and  con- 
taining an  excess  of 
NH4NO3  and  precip- 
itant. Chlorides,  HCi, 
reducing  agents  and  or- 
ganic acids  should  be 
absent. 

S,S02, 

SoOg, 

So,', 

etc. 

Weigh- 
ing 

Precipitant  BaCl2  in  hot 
solution  containing  a 
little  free  HC1. 

BaS04 

Same  as  BaSO4. 

Cl 

Weigh- 
ing 

Precipitant  AgNO3. 

AgCl 

Same  as  Ag. 

Si  and 
SiOa 

Weigh- 
ing 

By  evaporation  of  acid 
solution  to  dryness  and 
heating  at  115°  to  120°  C., 
or  by  evaporation  of 
H2SO4  solution  to  fumes 
of  SOS. 

xH3O,Si03 

Should  contain  HCI.  If 
much  HNO3  is  present, 
should  be  removed  by 
adding  HCI  and  boiling. 

C,C02, 
etc. 

Weigh- 
ing 

Absorption  with  KOH, 
NaOH,  or  CaOH  + 
NaOH. 

Na2CO3,  KoCOgor 
Na2C03  +  CaC03 

N 

Weigh- 
ing 

PtCl4 

(NH4)2PtCl« 

Same  as  KaPtCl6. 

TABLES. 


PRECIPITATES. 


Soluble  in  — 

Contaminants. 

Prepared  for 
Weighing  by  — 

Weighed 
as— 

Soluble    in    alkaline    hy- 
drates,   carbonates,   and 
sulphides.     In  KHSO3, 
in    aqua    regia,    and    in 
H20  +  Clor  H20  +  Br. 
In  warm  acids.     In   H2O 
+  NH4C1      Insoluble   in 
NH4Ori  +  alcohol. 

Other  sulphides  of  H2S 
group  if  present. 

Basic  Mg  salts,  sulphates, 
and  other  salts  insoluble 
in  NH4OH  +  alcohol. 

Drying.  Volatile  as 
As2S3  upon  ignition. 

Dissolving  the  precip- 
itate in  HNOS  into  a 
weighed  vessel,  evapo- 
rating, and  igniting 
slowly  at  first. 

As2S3 
Mg2As2O7 

Moderately  concentrated 
acids  (HC1  especially). 
Tartaric  acid  assists  pre- 
cipitation. Dissolved  by 
fixed  alkalies  or  alkaline 
sulphides. 

S  generally  accompanies 
the  precipitate;  removed 
by  replacing  the  H2O  by 
alcohol,  and  washing 
with  CS2. 

Mixed  with  50  times  its 
weight  of  HgO,  and 
ignited  to  dull  red. 

Sb2O4 

Moderately  strong  acids 
(HC1  especially).  In 
boiling  solution  contain- 
ing free  H2C2O4. 

Other  members  of  H2S 
group,  if  present.  Sepa- 
rated from  Sb2S3  by  add- 
ing H2C2O4,  and  boiling. 

Heating  moderately  and 
slowly  with  free  access 
of  air.  Addition  of 
HNO3'aids  conversion. 

SnO2 

Same  as  Mg. 

NH4OH  and  alkalies. 
Soluble  in  HC1  and  mod- 
erately strong  H2SO4 
or  HNO3.  In  hot  H2O. 
Insoluble  in  very  dilute 
HNO3  containing  NH4 
N03. 

Same  as  Mg. 

Arsenio-molybdate,  SiO2  , 
Fe203  ,  and  TiO2. 

Same  as  Mg. 

For  titration  by  dissolv- 
ing in  NH4OH  and 
reducing  by  Zn  -}- 
H2SO4  ,  or  by  acidim- 
etry. 

Mg2P207 

Same  as  BaSO4. 

Same  as  BaSO4. 

Same  as  BaSO4. 

BaS04 

Same  as  Ag. 

Same  as  Ag. 

Same  as  Ag. 

AgCl 

Boiling  caustic  fixed  al- 
kalies. By  fusion  with 
fixed  alkalies  (caustic  or 
carbonate).  Insoluble  in 
H2O  and  acids  (HF  ex- 
cepted). 

Insoluble  sulphates,  re- 
moved by  digestion  with 
cone.  H2SO4.  Also 
SnO2,  Sb2O4.andTiO2. 
Sometimes  A12O3  and 
Fe2O3.  In  which  case 
determine  by  loss. 

Ignition  after  drying. 
When  impurities  are 
present  is  determined 
by  loss  on  ignition 
with  HF  and  H2SO4. 

SiOa 

H2O  and  CO2  from  the 
atmosphere.  Prevented 
by  suitable  absorption 
apparatus. 

Absorption  in  weighed 
apparatus  containing 
suitable  absorbents. 

C03 

Same  as  K2PtCl8. 

Same  as  K2PtCl6. 

Ignition  to  Pt. 
(See  K2PtCl«.) 

Pt 

368 


A   MANUAL    OF  PRACTICAL   ASSAYING. 


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AgNOs  +  NaC 


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AgBr  +  NaNO8 
AgCNS  +  KNO 


AgN03  +  NaB 
gN03  +  KCNS 


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ipitated  MnO2  i 
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he  precipitated  i2MoO3(NH4)3  ,  PO4 
is  dissolved  in  NH4OH,  an  excess  of 
H2SO4  is  added,  and  the  MoO3  re- 
duced by  Zn.  The  reduced  Mo12Oj8 
is  then  determined  by  titration. 

he  precipitated  !2MoO3(NH4)3PO4 
is  treated  with  an  excess  of 
standard  NaOH,  and  the  excess  of 
NaOH  determined  by  alkalimetry. 

he  SO3  is  precipitated  from  a  solu- 
tion slightly  acid  with  HNO3  by 
Pb(NO3)2  ,  and  the  Pb  combined  as 
PbSO4  determined  by  titration. 

he  evolved  H2S  is  absorbed  by  an 
alkaline  solution  of  CdSO4.  The 
S  combined  as  CdS  is  determined 
(after  solution  of  the  CdS  in  HCI) 
by  titration. 

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APPENDIX  A. 


MELTING  AND  REFINING  GOLD  BULLION. 

THE  melting  and  refining  of  gold  bullion  and  the  prepara- 
tion of  gold  amalgam  for  retorting  are  operations  which  appear 
to  be  imperfectly  understood  by  many  mill  superintendents,  if 
one  judges  by  the  frequency  with  which  extremely  base  bullion 
is  deposited  at  the  government  mints  and  assay  offices. 

Deposits  of  gold  bullion  may  be  classed  as  follows :    . 

Grains,  generally  the  result  of  placer  washing.  The  gold  is 
usually  quite  fine  and  free  from  impurities  other  than  sand. 
Placer  gold  frequently  contains  small  quantities  of  lead  and 
occasionally  sulphides,  especially  if  derived  from  streams  below 
stamp  mills.  Another  class  of  grains  are  those  derived  from 
the  washing  of  small  pockets  of  very  rich  ores  which  are  some- 
times encountered  in  veins.  These  frequently  carry  pyrite 
and  other  minerals  which  were  associated  with  the  gold  in 
the  ore. 

Amalgamated  grains,  generally  derived  from  placer  wash- 
ing. As  many  placer  miners  working  on  a  small  scale  have 
but  imperfect  facilities  for  retorting  the  amalgam,  these  grains 
frequently  contain  mercury  in  addition  to  sand  and  clay. 

Retorts,  generally  the  result  of  stamp  mill  operations.  If 
the  result  of  the  treatment  of  free  ores  these  are  generally 
quite  free  from  impurities  other  than  sand.  If  the  result  of 
the  treatment  of  sulphide  ores  they  frequently  contain  lead, 
copper,  arsenic,  and  sulphides.  The  retort  gold  from  Gilpin 
county,  Colorado,  while  generally  the  result  of  the  treatment  of 
sulphide  ores,  is  usually  quite  free  from  large  amounts  of  these 
impurities,  showing  care  in  the  preparation  and  retorting  of 

371 


372  APPENDIX  A. 

the  amalgam.  Retorts  are  occasionally  received  which  con- 
tain large  quantities  of  water  and  mercury,  showing  great  care- 
lessness on  the  part  of  those  intrusted  with  the  preparation  of 
the  bullion.  The  base  character  of  retorted  bullion  is  some- 
times due  to  the  employment  of  foul  quicksilver  in  milling. 
As  quicksilver  is  readily  purified,  and  as  the  use  of  foul 
"  quick  "  invariably  results  in  the  loss  of  gold,  this  practice 
cannot  be  condemned  too  severely. 

Bars,  which  may  be  the  result  of  amalgamation,  chlorina- 
tion,  leaching,  smelting  or  placer  washing.  The  bars  from 
amalgamation  usually  contain  the  same  impurities  as  the  re- 
torts, unless  they  have  been  subjected  to  thorough  refining 
during  melting,  which  is  not  generally  the  case.  Bars  from 
chlorination  works  generally  contain  copper,  sulphides  (where 
sulphuretted  hydrogen  is  the  precipitant  employed),  iron  (where 
ferrous  sulphate  is  the  precipitant  employed),  and  more  or  less 
lead.  Arsenic  is  also  a  constituent  of  these  bars  from  some 
works. 

Bars  from  leaching  works  usually  contain  the  same  im- 
purities as  those  from  chlorination  and  also  zinc  (where  zinc  is 
the  precipitant  employed,  as  is  usual  where  the  cyanide  process 
of  extraction  is  used).  These  bars  are  frequently  very  base 
and  difficult  to  refine. 

Bars  from  smelters  may  be  divided  into  two  classes  :  parted 
or  fine  bars  and  unparted  bars,  the  latter  frequently  being  un- 
refined. The  parted  bullion  generally  contains  no  impurities 
worth  mentioning,  small  amounts  of  silver  and  copper,  to- 
gether with  the  gold  (usually  over  990  fine),  constituting  the 
bullion.  Occasionally  small  amounts  of  lead  (sufficient  to 
render  the  bullion  brittle)  are  present.  Unrefined  bullion  from 
smelters  frequently  contains  copper,  arsenic,  lead,  and  various 
elements  which  were  constituents  of  the  ores. 

Jewelry  and  old  plate,  which  is  generally  deposited  in  the 
form  of  bars  or  kings.  These  usually  contain  considerable 
amounts  of  silver  and  copper,  but  are  otherwise  quite  pure. 
Iron  (from  watch  springs,  etc.)  is  sometimes  present. 

All  of  these  deposits,  except  the  parted  bars  and  those 


APPENDIX  A.  373 

derived  from  chlorinatiori  and  leaching,  contain  considerable 
amounts  of  silver  and  require  parting  prior  to  coinage.  These 
are  the  principal  impurities,  although  other  elements,  as  bis- 
muth, antimony,  tellurium,  etc.,  are  frequently  present  in  small 
quantities. 

EFFECT   OF  IMPURITIES. 

Antimony,  arsenic,  lead,  sulphur,  tellurium,  and  zinc  ren- 
der the  gold  brittle  and  unfit  for  rolling,  even  when  present  in 
such  small  quantities  as  ^Vo  Part-  Zinc,  when  added  to  gold 
in  large  quantities,  produces  a  ductile  alloy. 

Iron,  aluminum,  nickel,  cobalt,  platinum,  palladium,  and 
rhodium  form  ductile  alloys  with  gold. 

The  presence  of  lead  is  indicated  by  the  fracture,  which  is 
granular  and  has  a  silver-white  lustre.  The  fracture  of  bullion 
containing  arsenic  is  the  same  except  that  the  color  is  a  gray- 
ish white,  resembling  the  color  of  metallic  lead.  The  fracture 
of  bullion  containing  zinc  is  crystalline  to  granular,  and  has  a 
dirty- white  color  ;  such  bullion  is  seldom  homogeneous.  Bull- 
ion containing  sulphides  has  a  dirty  dark-gray  granular  frac- 
ture. Small  amounts  of  tellurium  render  the  bullion  crystal- 
line, the  fracture  resembling  the  crystalline  structure  of 
metallic  tellurium. 

When  the  bullion  contains  lead,  bismuth,  and  zinc  there  is 
a  liquation,  or  separation,  of  these  metals  towards  the  outside 
of  the  bar  on  casting. 

Iridium  and  osmium  separate  to  the  bottom  of  the  melt. 

Platinum  separates  to  the  centre  of  the  bar. 

If  the  bullion  is  free  from  impurities  other  than  silver  and 
copper,  simple  melting  is  all  that  is  necessary  in  order  to  pro- 
duce a  ductile  and  homogeneous  bar.  Should  other  impurities 
be  present  they  must  be  removed  by  refining. 

MELTING. 

The  bullion  is  melted  in  clay,  sand,  or  graphite  cruci- 
bles. It  is  usual  to  place  the  crucible  in  which  the  melting  is 


374  APPENDIX  A. 

performed  inside  of  a  larger  graphite  crucible  in  order  to  avoid 
danger  of  loss  should  the  melting-pot  crack  or  break. 

A  wind  furnace  using  coke  or  charcoal — the  latter  is  prefer- 
able— serves  all  purposes,  but  where  many  melts  are  made  the 
gas  furnace  is  to  be  preferred  on  account  of  the  facility  with 
which  the  temperature  can  be  controlled. 

The  crucible  should  be  heated  gradually  in  order  to  avoid 
its  destruction  by  cracking,  and  finally  at  a  high  temperature. 

The  bullion  is  now  introduced,  the  crucible  is  covered,  and 
the  temperature  is  raised.  A  plumbago  stirrer  is  placed  in  the 
furnace  so  that  when  the  bullion  is  melted  the  stirrer  will  be 
hot.  This  stirrer  is  a  bar  of  plumbago  about  8  inches  long,  i^ 
inches  wide,  and  f  inch  thick,  and  is  slightly  curved  and  flat- 
tened at  one  end  to  facilitate  the  removal  of  slag.  When  the 
bullion  has  melted  down  and  is  perfectly  fluid  the  cover  is  re- 
moved from  the  crucible.  If  pure,  the  surface  of  the  melt 
should  be  perfectly  clear,  and  present  the  appearance  of  a 
mirror.  If  not  clear,  refining  is  necessary.  If  clear,  the  melt 
is  thoroughly  stirred  when  it  is  ready  for  casting.  The  cruci- 
ble is  removed  from  the  furnace  and  its  contents  are  quickly 
poured  into  an  iron  mould  which  has  previously  been  heated 
and  greased  with  beeswax.  In  order  to  avoid  loss  by  spatter- 
ing, the  mould  should  not  be  filled  more  than  two  thirds.  The 
mould  is  covered,  and  as  soon  as  the  bullion  solidifies  the  bar 
is  turned  out  and  immersed  in  a  bath  of  dilute  sulphuric  acid. 
This  operation,  called  "  pickling,"  serves  to  remove  any  slight 
stain  from  the  surface  of  the  bar,  and  gives  it  a  handsome  ap- 
pearance. Some  operators  use  a  dilute  solution  of  nitric  acid 
for  this  purpose.  Should  the  bar  show  slight  sulphide  stains 
they  may  be  removed  by  washing  with  a  dilute  solution  of 
potassium  cyanide.  After  pickling,  the  bar  is  washed  in  water, 
and  any  adhering  slag  is  removed  by  hammering  and  washing. 

REFINING. 

Impure  bullion  may  be  refined  by  fluxing  in  the  crucible, 
by  cupellation,  or  by  parting  in  acids  after  melting  with  suffi. 


APPENDIX  A.  375 

cient  silver  to  insure  parting.  Parting  is  generally  preceded 
by  cupellation  or  crucible  refining. 

Crucible  Refining. — After  the  bullion  has  been  melted  as 
above,  it  is  subjected  to  the  action  of  certain  fluxes  for  the  re- 
moval of  the  impurities.  Sand  is  removed  by  the  addition  of 
borax-glass,  or  borax-glass  and  sodium  bicarbonate,  to  the  melt, 
the  resulting  slag  being  lifted  off  with  the  stirrer.  The  stirrer 
should  be  of  the  same  temperature  as  the  furnace,  in  which  it 
should  remain  throughout  the  operation.  Iron  and  black  sand 
are  removed  in  the  same  manner.  When  much  iron  is  present 
.it  may  be  removed  by  fluxing  with  sulphur.  After  the  gold  is 
melted  sulphur  is  thrown  around  the  sides  of  the  melt,  care 
being  taken  to  add  the  sulphur  to  the  sides  of  the  melt. 
Should  the  sulphur  be  thrown  on  the  centre  there  is  liability  of 
loss  of  gold,  owing  to  the  violent  action  which  ensues.  The 
temperature  should  not  be  much  above  the  melting-point  of 
the  bullion,  as  otherwise  there  will  be  an  undue  loss  of 
sulphur.  The  sulphur  is  stirred  into  the  melt  with  the  plum- 
bago stirrer,  and  forms  iron  matte,  which  rises  to  the  surface. 
The  operation  is  continued  until  all  the  iron  is  eliminated  as 
matte,  when  the  bullion  and  matte  are  cast.  The  matte  will 
be  found  on  the  surface  of  the  bar,  and  is  readily  removed. 
This  matte  should  be  fused  with  borax  and  soda,  the  result  of 
the  fusion  being  a  button  of  bullion  and  clean  matte,  which 
may  be  discarded.  The  button  and  bar  are  now  melted  to- 
gether with  nitre  and  borax,  the  result  being  a  clean  bar  of 
bullion.  As  long  as  the  melt  contains  iron  but  little  silver 
sulphide  will  be  formed  ;  hence,  as  soon  as  the  iron  has  all 
been  converted  into  matte  the  addition  of  sulphur  should  be 
discontinued. 

Lead  is  removed  by  the  oxidizing  action  of  nitre  which  is 
thrown  on  the  surface  of  the  melt  from  time  to  time.  Borax- 
glass  is  added  with  the  nitre,  to  stiffen  the  slag  and  render  its 
removal  easy.  Towards  the  end  of  the  operation  the  surface 
of  the  melt  presents  a  play  of  colors  as  in  cupellation,  and  after 
this  ceases  fine  threads  may  be  seen  continually  crossing  each 
other.  The  lead  is  now  nearly  all  removed  and  the  bullion  is 


376  APPENDIX  A. 

liable  to  bubble  or  boil  at  this  stage,  but  soon  becomes  quiet 
and  perfectly  clear,  when  it  is  ready  for  casting.  Small  quan- 
tities of  lead  are  readily  removed  by  the  addition  of  oxide  of 
copper,  but  some  refiners  object  to  the  use  of  this  reagent,  as 
it  introduces  copper  into  the  bullion.  Should  the  amount  of 
lead  present  be  large,  the  oxidation  by  nitre  will  be  tedious. 
When  large  quantities  of  lead,  arsenic,  or  sulphides  are  present, 
bichloride  of  mercury  may  be  used  to  advantage.  The  salt  is 
broken  into  small  lumps,  which  are  thrown  on  the  melt  from 
time  to  time.  The  bichloride  sinks  into  the  melt,  where  it  is 
decomposed,  the  liberated  chlorine  permeating  the  liquid  mass 
and  rapidly  oxidizing  the  impurities.  This  reagent  should 
never  be  used  except  where  the  furnace  is  provided  with  a  wide 
throat,  a  strong  draft,  and  a  hood  to  carry  off  any  fumes  which 
may  escape.  On  account  of  the  dangerous  nature  of  the  fumes, 
this  reagent  is  not  largely  used.  Ammonium  chloride  is  also 
used,  but  its  action  is  much  less  rapid  than  that  of  the  mercury 
salt.  At  the  Royal  Australian  mint  chlorine  gas  is  forced 
through  the  liquid  melt  both  for  the  removal  of  impurities  and 
silver,  the  chlorine  oxidizing  the  impurities  and  converting  the 
silver  into  a  chloride  which  rises  to  the  surface. 

Arsenic  is  removed  in  the  same  manner  as  lead,  it  rising  to 
the  surface  of  the  melt  in  the  form  of  small,  oily  globules. 

Sulphur  is  removed  in  the  same  manner  as  lead  and  arsenic, 
but  should  the  amount  present  be  large  the  operation  will  be 
tedious  and  the  following  method  may  be  adopted  to  ad- 
vantage :  Prepare  some  strips  of  strap  iron  and  as  soon  as  the 
bullion  is  melted  introduce  them  into  the  crucible.  The  iron 
decomposes  the  sulphides,  forming  an  iron  matte,  which  rises 
to  the  surface.  The  matte  is  removed  by  skimming  and  is  put 
aside  for  future  treatment.  This  treatment  is  continued  until 
the  sulphides  are  all  decomposed,  when  the  bullion  and  slag 
are  poured  off  into  a  mould.  After  chilling,  the  matte  is  re- 
moved and  added  to  the  skimmings,  the  whole  being  melted 
in  a  crucible,  together  with  borax  to  recover  the  shots  of  gold 
which  it  contains.  The  result  of  this  melt  will  be  a  king  of 
bullion  and  clean  matte  or  slag  which  may  be  discarded.  The 


APPENDIX  A.  377 

bar  and  king  are  now  melted  with  nitre,  and  the  small  amount 
of  sulphides  present  are  removed  by  refining  with  nitre  and 
borax.  The  result  of  this  melt  is  generally  a  refined  bar,  al- 
though a  third  melting  with  nitre  is  sometimes  necessary. 

Platinum  is  partially  removed  by  the  action  of  nitre,  some 
passing  into  the  slag,  but  the  greater  portion  remains  with  the 
gold  and  must  be  removed  by  subsequent  acid  refining. 

Iridium  and  osmium,  commonly  called  osmiridium,  as  the 
metals  occur  together  and  remain  together  during  treatment, 
may  be  removed  by  fire  refining.  The  bullion  is  melted  and 
allowed  to  remain  in  the  crucible  for  half  an  hour  at  a  high 
temperature.  The  osmiridium  liquates  and  sinks  to  the  bottom 
of  the  crucible.  The  furnace  is  then  chilled  and  as  soon  as  the 
bullion  solidifies  it  is  turned  out  of  the  crucible.  The  osmirid- 
ium is  found  at  the  bottom,  alloyed  with  gold  and  silver,  and 
is  cut  off.  As  the  osmiridium  settles  better  from  an  alloy 
consisting  chiefly  of  silver,  the  rich  buttons  are  repeatedly 
melted  with  silver,  the  lowest  portion  being  cut  off  each  time. 
The  alloy  finally  obtained  is  granulated  and  parted,  the  silver 
passing  into  solution  and  the  osmiridium  remaining  behind, 
together  with  the  small  amount  of  gold  remaining  in  the  alloy. 

Antimony  is  best  removed  by  treatment  with  metallic  iron, 
as  in  the  case  of  sulphides. 

Another  method  of  crucible  refining  which  is  sometimes 
adopted  is  as  follows:  The  bullion  is  melted  in  a  plumbago 
or  clay  crucible,  and  when  fluid  the  surface  of  the  melt  is 
covered  with  bone-ash.  Small  quantities  of  lead  are  forced 
into  the  molten  mass,  usually  from  o.i  to  I.  per  cent,  of  lead 
being  sufficient.  The  lead  is  thoroughly  stirred  into  the  mass, 
and  nitre  is  added  as  an  oxidizing  agent  from  time  to  time. 
The  effect  of  the  nitre  is  to  oxidize  the  lead  and  the  impurities 
which  rise  to  the  surface  and  are  absorbed  by  the  bone-ash. 
Sometimes  oxide  of  copper  or  metallic  copper  (about  twice 
the  weight  of  lead  used)  is  added  to  advantage,  especially  if 
the  bullion  contains  zinc.  The  operation  is  virtually  that  of 
cupellation. 


APPENDIX  A. 

Other  impurities  are  generally  present  in  small  amounts  and 
are  readily  removed  by  nitre  and  borax. 

Potassium  nitrate  is  the  reagent  generally  employed,  as  the 
commercial  sodium  salt  is  not  nearly  as  pure  and  generally 
contains  considerable  chloride  of  sodium.  Should  much  silver 
be  present,  chloride  of  sodium  is  liable  to  result  in  loss  by 
volatilization. 

The  refining  is  preferably  performed  in  clay  or  sand  cruci- 
bles. When  only  graphite  crucibles  are  at  hand,  or  where  the 
melt  is  too  large  for  the  clay  or  sand  crucibles,  the  refining 
may  be  carried  on  in  a  graphite  melting-pot,  the  corroding 
effects  of  the  nitre  and  slag  on  the  graphite  being  lessened  by 
throwing  bone-ash  on  the  surface  of  the  melt.  This  collects 
around  the  sides,  absorbs  oxides,  and  forms  a  ring  around  the 
sides  of  the  crucible  which  effectually  protects  them. 

Refining  by  Cupellation. — When  large  amounts  of  lead, 
arsenic,  sulphur,  etc.,  are  present,  crucible  refining  is  slow  and 
tedious,  and  cupellation  may  be  substituted  to  advantage. 
Where  a  cupel  furnace  is  not  at  hand  a  very  good  substitute 
may  be  readily  arranged  as  follows :  Saw  off  the  lower  part  of 
a  graphite  melting-pot  about  four  inches  above  the  bottom  and 
tamp  in  with  bone-ash.  Hollow  out  the  cupel  to  receive  the 
metal  and  place  it  in  the  throat  of  a  wind  furnace  provided 
with  a  good  charcoal  fire.  When  the  cupel  is  hot  introduce 
the  bullion,  together  with  sufficient  lead,  place  the  cover  on 
the  furnace,  and  give  the  fire  a  strong  draft.  As  soon  as  the 
lead  begins  to  drive,  the  cover  is  removed  from  the  furnace, 
the  operation  requiring  no  further  attention  other  than  to  keep 
the  temperature  at  such  a  point  that  there  is  no  chance  of  the 
metal  solidifying  or  freezing  before  the  lead  is  all  removed. 
Should  the  metal  chill  before  the  lead  is  entirely  removed,  the 
small  amount  remaining  may  readily  be  removed  by  subse- 
quent crucible  refining. 

Where  a  large  muffle  furnace  is  at  hand  cupellation  may  be 
readily  carried  on  in  the  muffle  by  preparing  some  large 
cupels  8  to  10  inches  in  diameter,  which  are  placed  in  the 
muffle,  and  when  hot  the  bullion  is  introduced,  together  with 


APPENDIX  A.  379 

sufficient  lead  to  effect  cupellation.  The  cupels  are  made  of 
bone-ash  thoroughly  tamped  in  around  a  circular  iron  ring; 
and  subsequently  thoroughly  seasoned  by  slow  drying.  A 
good  substitute  for  the  iron  ring  is  a  circular  section  sawed  out 
of  an  old  graphite  melting-pot.  In  this  way  from  one  to  two 
hundred  ounces  of  bullion  may  be  easily  and  quite  thoroughly 
refined.  The  cupel  bottoms  should  be  saved,  as  they  are 
liable  to  absorb  precious  metals,  which  is  especially  the  case 
when  the  bullion  contains  much  ^inc,  copper,  sulphides,  and 
tellurium. 

Acid  Refining. — Whilst  acid  refining  or  parting  is  usually 
preceded  by  crucible  refining  or  cupellation,  this  method  is 
sometimes  adopted  preliminary  to  fire  refining.  Treatment 
with  sulphuric  acid  prior  to  melting  is  especially  efficient  for 
the  removal  of  zinc  from  the  gold  slimes,  or  precipitate,  ob- 
tained on  zinc  shavings  in  the  extraction  of  gold  by  the  cy- 
anide process.  Whilst  the  action  of  sulphuric  is  slower  than 
that  of  hydrochloric  acid,  and  the  sulphate  solution  is  more 
tedious  to  filter,  the  use  of  the  former  acid  is  preferable  on  ac- 
count of  the  liability  of  loss  of  gold  owing  to  the  generation  of 
free  chlorine  during  the  treatment  with  hydrochloric  acid. 
Commercial  hydrochloric  acid  is  also  liable  to  contain  some 
nitric  acid,  which  would  involve  loss  of  gold  if  present.  Direct 
treatment  of  the  slimes  with  acid  is  unsatisfactory,  owing  to 
the  loss  of  gold  due  to  the  evolution  of  hydrocyanic  acid  and 
the  formation  of  gelatinous  cyanide  of  zinc,  which  latter 
renders  the  filtration  extremely  tedious  and  difficult.  If  the 
slimes  are  previously  treated  in  a  filter  press  (Johnson's*)  the 
soluble  cyanide  salts  may  be  readily  separated  by  washing,  the 
bulk  of  the  zinc  being  thus  removed  in  solution.  The  residues 
are  now  spread  in  thin  layers  on  iron  trays,  and  dried  and 
heated  at  a  barely  perceptible  red  heat  in  the  muffle  or  the  flue 
of  a  furnace.  The  carbon,  zinc,  arsenic,  etc..  ignite  readily, 
being  in  a  fine  state  of  division,  and  the  roasting  proceeds 
with  regularity  to  the  bottom  of  the  layer  without  stirring. 


*The  Lixiviation  of  Silver  Ores.     Stetafeldt.  (Scietif.  Pub.  Co.). 


380  APPENDIX  A. 

The  resulting  mass  is  oxidized,  porous  and  aggregated  some- 
what into  granules.  This  mass  consists  principally  of  oxides 
of  lead  and  zinc  with  gold  and  silver.  It  is  now  ready  for 
treatment  by  heating  with  dilute  sulphuric  acid,  the  zinc  pass- 
ing into  solution,  leaving  the  gold  and  silver  behind,  together 
with  lead  sulphate.  This  residue  is  easily  filtered  and  washed, 
when,  after  drying,  it  is  fused  with  nitre,  borax  and  bicarbonate 
of  soda.  The  method  of  crucible  cupellation  may  also  be  ad- 
vantageously used. 

Acid  refining  in  nitric  or  sulphuric  acids,  after  melting  with 
sufficient  silver  and  granulating,  is  extremely  efficient,  but  as 
this  method  requires  a  special  plant  and  is  moreover  described 
in  the  standard  works  on  the  metallurgy  of  gold  and  silver,*  it 
is  unnecessary  to  discuss  it  here. 

Toughening. — All  bullion  requires  toughening  to  render  it 
perfectly  ductile.  This  is  usually  accomplished  by  melting 
with  nitre  and  borax,  with  potassium  bisulphate  and  borax,  or 
by  the  addition  of  bichloride  of  mercury  to  the  melt.  It  may 
also  be  accomplished  by  forcing  chlorine  gas  through  the 
molten  mass  or  by  pouring  the  molten  gold  in  a  thin  stream 
through  the  air  from  a  height  of  three  or  four  feet. 

Bullion  which  has  been  thoroughly  refined  will  consist  of 
an  alloy  of  gold  and  silver,  with  possibly  some  copper,  and 
should  be  ductile  and  perfectly  homogeneous.  Brittle  bullion 
may  be  homogeneous,  but  more  frequently  samples  taken  from 
different  parts  of  the  bar  will  show  considerable  differences  in 
fineness. 

SAMPLING. 

Either  of  the  following  methods  is  to  be  recommended : 
Cutting  off  diagonally  opposite  corners  with  a  chisel.  These 
clips  are  pounded  on  a  polished  steel  anvil  and  passed  through 
a  set  of  hand  rolls  until  rolled  into  the  form  of  a  ribbon. 

*  The  Metallurgy  of  Gold  and  Silver  in  the  United  States.  Egleston.  (Wiley 
&  Sons.) 

Precious  Metals  in  the  United  States.  Report  of  the  Director  of  the  Mint. 
Washington,  1880. 

The  Metallurgy  of  Gold.     T.  Kirk  Rose.     London,  1894. 


APPENDIX  A.  381 

Drilling,  it  being  preferable  to  take  four  drillings  as  indi- 
cated in  the  sketch.  Equal  amounts  of  the  a,  af  drillings  are 
mixed  together  for  the  a  sample.  The  b,  bf  drillings  are  treated 
in  the  same  manner  for  the  b  sample. 

Where  the  bar  is  ductile  and  perfectly  homogeneous  the 
first  method  is  preferable  as  the  sample  is  in  better  condition 
for  rapid  weighing  out. 

Where  the  bullion  is  brittle  and  probably  not  homogeneous 
samples  taken  be  the  second  method  will  more  truly  represent 
an  average  of  the  bar. 

Another  method  which  may  be  adopted  to  advantage  in 
the  case  of  very  impure  bullion  is  to  take  dip  samples  from  the 
molten  mass  in  the  crucible.  One  sample  is  taken  just  before 
pouring  and  after  skimming.  A  second  sample  is  taken  when 
nearly  all  the  bullion  has  been  poured.  A  convenient  vessel 
for  taking  the  sample  is  a  small  Hessian  crucible  or  a  plumbago 
cup  which  is  made  especially  for  this  purpose.  Each  sample  is 
granulated  by  pouring  into  water,  the  granulations  being  kept 
separate. 


jo 


1 

x^fe" 

6 

FIG.  i.  FIG.  2. 


APPENDIX  B. 


THE  PREPARATION  OF  PURE  GOLD  AND  SILVER. 

PURE  gold  and  silver  are  necessary  in  the  assay  of  gold 
bullion  (Part  III.,  Chapter  III.)  and  are  also  frequently  used  in 
the  assay  of  ores  and  metallurgical  products.  Pure  silver  may 
be  purchased  from  dealers,  but  gold  of  sufficient  purity  is  not 
readily  obtained. 

The  Preparation  of  Proof  Gold. — As  pure  gold  as  is  ob- 
tainable should  be  taken  for  the  preparation  of  the  proof  ma- 
terial. The  best  material  to  use  is  the  gold  cornets  obtained  in 
the  assay  of  gold  bullion  and  the  parted  gold  resulting  from  the 
assay  of  gold  ores.  These  cornets  are  about  998  fine  and  the 
other  0.002  parts  being  silver.  Should  such  material  be  unob- 
tainable, material  of  similar  quality  may  be  prepared  from  gold 
coin  or  refined  bullion  as  follows :  Weigh  out  the  gold  and  for 
each  part  of  gold  add  2j  parts  of  pure  silver  and  from  10  to 
16  parts  of  pure  lead.  Cupel,  and  after  flattening  the  result- 
ing button  of  gold  and  silver,  anneal  it  at  a  red  heat.  The 
button  is  now  passed  through  the  flattening  rolls  until  reduced 
to  a  ribbon  of  about  the  thickness  of  a  fine  visiting  card.  The 
ribbon  is  annealed,  rolled  into  a  coil,  introduced  into  a  flask 
containing  nitric  acid  of  27°  B.  and  boiled  for  20  minutes. 
The  solution  is  poured  off  and  fresh  acid  of  32°  B.  is  added  in 
which  the  ribbon  is  boiled  for  20  minutes.  The  acid  is  poured 
off  and  the  ribbon  is  washed  several  times  with  distilled  water. 
In  this  treatment  the  copper  and  other  impurities  are  removed, 
the  ribbon  consisting  of  gold  and  a  small  amount  of  silver. 

The  gold  taken  is  weighed  and  introduced  into  an  Erlen- 
ineyer  flask  and  aqua-regia  is  added.  About  4  fluid  ounces  of 

382 


APPENDIX  B. 

acid  will  be  required  for  each  Troy  ounce  of  gold  taken.  The 
acid  is  added  gradually,  and  after  all  is  added  the  flask  is  heated 
over  a  Bunsen  burner  protected  with  a  piece  of  asbestos  card- 
board. When  the  gold  is  all  dissolved  the  contents  of  the 
flask  are  slightly  diluted  with  distilled  water  and  allowed  to 
stand  for  a  few  hours  to  allow  the  separated  silver  chloride  to 
settle.  The  clear  solution  is  now  decanted  off  into  a  large 
porcelain  evaporating  dish,  care  being  taken  to  retain  the  silver 
chloride  in  the  flask.  The  contents  of  the  dish  are  evaporated 
until  all  the  nitric  and  most  of  the  free  hydrochloric  acid  is 
expelled.  At  this  point  auric  chloride  will  commence  to  sepa- 
rate out.  The  solution  is  largely  diluted  with  distilled  water 
and  filtered  through  a  heavy  filter  paper  into  a  large  glass 
flask.  The  solution  in  the  flask  is  diluted  with  distilled  water 
until  the  flask  contains  as  many  litres  as  there  are  ounces  of 
gold  in  solution.  The  neck  of  the  flask  is  covered  and  its  con- 
tents are  allowed  to  stand  for  five  or  six  days  in  order  that  the 
silver  chloride  may  settle  and  separate.  The  clear  solution  is 
now  decanted  through  a  triple  filter  paper  into  a  glass  flask. 
The  precipitate  and  a  small  portion  of  the  solution  should  be 
allowed  to  remain  in  the  flask,  for  if  washed  onto  the  filter, 
there  is  danger  of  silver  chloride  passing  through  into  the  fil- 
trate. The  filtrate  is  heated  nearly  to  boiling  and  an  excess  of 
a  saturated  solution  of  oxalic  acid  is  added.  The  flask  is 
allowed  to  stand  in  a  warm  place  over  night,  when,  provided 
sufficient  oxalic  acid  was  added,  the  solution  will  be  found  to 
be  colorless,  showing  that  all  the  gold  has  been  precipitated. 
The  solution  is  poured  off  and  the  precipitated  gold  is  washed 
several  times  with  warm  distilled  water.  It  is  now  washed  with 
strong  ammonia-water  to  remove  any  trace  of  silver  chloride 
which  it  may  contain,  and  after  pouring  off  the  ammonia,  again 
with  water.  It  is  finally  washed  with  warm  dilute  hydrochloric 
acid,  and  after  pouring  off  the  acid,  again  with  distilled  water 
until  the  washings  are  sweet.  The  gold  is  now  washed  over 
into  a  porcelain  dish,  in  which  it  is  dried.  The  dry  gold  is 
melted  in  a  clay  crucible,  in  which  some  borax  has  previously 
been  fused  to  glaze  the  sides,  its  surface  being  protected  by  a 


384  APPENDIX  B. 

cover  of  borax-glass.  When  fluid  a  few  crystals  of  nitre  are 
added  and  stirred  into  the  melt  with  a  hot  plumbago  rod. 
The  melted  gold  and  slag  are  poured  into  a  hot  iron  mould 
which  has  previously  been  well  greased  with  beeswax,  and  as 
soon  as  it  solidifies  the  mould  is  turned  over  and  the  bar  is 
plunged  into  cold  water.  This  serves  to  remove  most  of  the 
slag,  the  remainder  being  removed  by  hammering  and  rubbing. 
The  bar  is  passed  through  a  set  of  flattening  rolls  until  rolled 
into  a  ribbon  of  convenient  thickness.  The  ribbon  is  rolled 
into  a  coil  which  is  boiled  in  dilute  hydrochloric  acid  and, 
after  pouring  off  the  acid,  it  is  washed  with  distilled  water, 
The  gold  is  finally  dried  and  heated  to  redness  in  the  muffle. 

In  this  manner  the  author  has  frequently  prepared  several 
ounces  of  gold  which  was  from  999.95  to  999.96  fine. 

Should  the  gold  used  contain  platinum  it  will  have  to  be 
removed.  To  remove  the  platinum  concentrate  by  evapora- 
tion the  clear  solution  of  chloride  of  gold  free  from  silver,  add 
an  excess  of  absolute  alcohol  and  pure  potassium  chloride  and 
allow  to  stand  at  least  24  hours.  Potassium  platinochloride 
will  separate  and  may  be  removed  by  filtration.  The  alcohol 
is  now  expelled  by  evaporation  when  the  solution  is  treated  PS 
before. 

Should  the  gold  contain  small  amounts  of  copper  it  may  be 
removed  from  the  solution  by  the  addition  of  caustic  potash, 
but  as  there  is  always  danger  of  its  incomplete  removal  the 
above  method  of  refining  by  cupellation  and  parting  is  prefer- 
able and  is  more  rapid. 

The  Preparation  of  Silver. — In  a  laboratory  where  many 
gold  assays  are  made  there  is  always  a  supply  of  chloride  of 
silver  on  hand  as  a  result  of  the  parting  operation,  the  nitric 
acid  solution  containing  silver  nitrate  being  decanted  from  the 
gold  into  a  glass  or  stone  vessel  containing  salt  (sodium  chlo- 
ride). This  silver  chloride  is  washed  with  water  until  the  wash- 
ings show  only  a  faint  trace  of  chlorides.  To  the  vessel  con- 
taining the  silver  chloride  there  are  now  added  several  strips 
of  sheet  zinc  (4  ounces  of  zinc  for  each  10  ounces  of  silver  wil) 
be  sufficient)  and  then  some  sulphuric  acid  of  60°  B.  The 


APPENDIX  B.  385 

vessel  is  allowed  to  stand  over  night,  and  if  sufficient  zinc  and 
acid  were  added,  the  silver  chloride  will  be  found  to  have  been 
all  converted  into  cement  silver.  Should  any  zinc  remain  un- 
dissolved,  more  sulphuric  acid  is  added  to  effect  its  solution. 
The  cement  silver  is  washed  with  water  until  the  washings 
are  sweet  and  is  then  dried.  It  is  melted  in  a  plumbago  cru- 
cible, the  silver  being  kept  covered  with  powdered  charcoal 
during  the  melting.  Should  the  silver  need  refining,  this  is 
accomplished  by  the  addition  of  nitre  and  borax-glass. 

The  melt  is  cast  into  a  bar  12  inches  long,  if  inches  wide 
and  £  inch  thick. 

For  the  silver  used  in  the  gold  bullion  assay  a  great  deal  of 
time  and  labor  may  be  saved  by  running  the  bar  through  a 
set  of  flattening  rolls  until  it  is  reduced  to  the  proper  thick- 
ness. The  rolled  strips  are  now  run  through  a  punching 
machine  which  punches  out  disks  of  definite  weights.  In  this 
manner  disks  of  silver  weighing  anywhere  from  500  milli- 
grammes to  25  milligrammes  maybe  cut.  They  will  be  found 
extremely  convenient  for  inquartation  of  the  alloy. 


APPENDIX  C. 

LOSSES    OF    GOLD   AND    SILVER    IN    THE    FIRE- 

ASSAY. 

As  this  is  a  question  of  considerable  commercial  importance 
as  well  as  of  scientific  interest,  a  review  of  the  results  bearing 
on  the  subject,  as  recently  obtained  by  the  author  and  others,* 
is  of  interest  in  connection  with  the  chapters  on  the  determina- 
tion of  gold  and  silver  in  ores  and  metallurgical  products. 

The  losses  of  gold  and  silver  in  the  fire-assay  are  due  to 
volatilization  and  slag  absorption  during  scorification  and 
fusion,  and  to  volatilization  and  cupel  absorption  during  cupel- 
lation.  The  following  also  have  an  influence  on  the  accuracy 
of  the  results : 

Inaccuracy  in  weighing  out  and  weighing  back.  The  small 
milligramme  weights  used  in  weighing  back  the  gold  and  silver 
beads  are  frequently  far  from  accurate.  Every  assayer  should 
thoroughly  test  each  set  of  weights  used,  as  those  purchased 
from  dealers  are  occasionally  far  from  accurate. 

Should  the  lead  buttons  contain  much  arsenic,  antimony, 
copper,  sulphides,  etc.,  the  cupellation  should  be  started  at  a 
high  temperature.  The  only  safe  method  to  adept  is  to  start 
the  cupellations  in  a  hot  part  of  the  furnace,  and  as  soon  as 
cupellation  commences  bring  the  cupels  forward.  Where 
impurities  are  present  the  results  will  be  low  unless  the  cupel- 
lation is  commenced  at  a  high  temperature.  After  cupellation 
is  thoroughly  started  the  cupels  should  be  brought  forward  in 

*  Furman:  Trans,  of  the  Am.  Inst.  of  Mining  Engineers,  Vol.  XXIV,  pp. 
735.  871,  and  874  ;  Ibid.,  Vol.  XXV.  Le  Doux:  Ibid.,  Vols.  XXIV  and  XXV. 
Mason  and  Bowman:  Journal  of  the  Am.  Chem.  Society,  Vol.  XVI,  p.  313, 
May,  1894.  Dewey:  Journal  of  the  Am.  Chem.  Society,  Vol.  XVI,  p.  505, 
August,  1894. 

386 


APPENDIX   C.  387 

the  muffle  so  that  the  cupellation  is  continued  at  compara- 
tively a  low  temperature,  and  so  that  the  cupels  show  feather 
litharge. 

Imperfect  elimination  of  the  base  metals  whilst  on  the 
cupel  is  a  frequent  cause  of  high  results.  This  is  especially 
the  case  where  the  lead  buttons  contain  copper.  The  only 
safe  plan  is  to  have  lead  buttons  which  are  perfectly  soft  and 
free  from  copper,  and  in  each  case  to  push  the  cupel  back  into 
a  hot  part  of  the  muffle  just  before  the  button  brightens,  and 
thus  brighten  at  a  high  temperature. 

Another  source  of  error  in  gold  assays  is  loss  of  gold  in 
parting,  and  imperfect  elimination  of  silver  from  the  gold  in 
parting.  The  first  source  of  error  is  always  due  to  careless 
manipulation  ;  the  second  is  due  to  carelessness  in  parting.  In 
order  to  insure  the  solution  of  the  silver  the  gold-silver  bead 
should  contain  at  least  three  and  a  half  parts  of  silver  to  each 
part  of  gold  present.  The  buttons  should  invariably  be  parted 
in  acids  of  two  different  strengths.  The  method  adopted  by 
the  author  is  to  part  in  nitric  acid  of  13°  Baume  until  all  action 
of  the  acid  has  apparently  ceased  ;  pour  off  this  acid,  and  boil 
in  nitric  acid  of  32°  Baume  for  four  minutes. 

The  size  of  the  lead  button  also  has  an  influence  on  the 
loss  in  cupellation.  An  excessively  large  button  will  cause  an 
excessive  loss.  A  button  weighing  from  7  to  8  grammes  is  the 
size  preferred  by  the  writer  for  ores  containing  up  to  300 
ounces  of  silver  and  5  ounces  of  gold  per  ton.  Such  a  button 
is  sufficiently  large  to  collect  all  the  precious  metals,  and  pre- 
sents the  advantage  that  it  is  on  the  cupel  but  a  short  time. 

The  weight  and  quality  of  the  cupel  used  also  have  an  in- 
fluence on  the  loss  in  cupellation.  The  cupel  should  weigh  at 
least  twice  as  much  as  the  button  to  be  cupelled  ;  it  should  be 
quite  hard  and  made  of  fine  bone-ash.  If  too  soft,  or  made  of 
coarse  bone-ash,  the  cupel  absorption  will  be  increased.  If  too 
hard  the  cupel  will  not  readily  absorb  the  litharge  formed. 
The  cupel  preferred  by  the  author  is  made  of  XX  bone-ash 
and  tamped  sufficiently  so  that  when  thoroughly  dry  it  will 
not  break  when  dropped  from  a  height  of  two  feet. 


388 


APPENDIX   C. 


The  temperature  during  fusion  or^  scorification  and  the 
character  of  the  slag  also  have  an  influence  on  the  losses  by 
slag  absorption.  The  fusions  should  be  started  at  a  compara- 
tively low  temperature  which  should  be  gradually  raised  to  a 
bright  red  at  the  finish.  The  fluxes  added  should  be  so  pro- 
portioned that  the  slag  will  be  perfectly  fluid,  pouring  clean 
and  thus  allowing  of  a  perfect  separation  of  the  slag  and 
button.  As  it  is  essential  that  the  charge  be  equally  heated 
throughout,  so  that  no  portion  commences  to  fuse  before 
another,  and  that  the  temperature  be  under  control,  the 
Colorado  practice  of  performing  the  fusions  in  the  muffle  is  to 
be  recommended.  The  essential  conditions  can  be  more 
readily  attained  in  the  muffle  than  in  the  wind-furnace. 

The  following  table  gives  the  results  of  Messrs.  Mason  and 
Bowman's  experiments  to  determine  the  losses  in  cupellation 
under  conditions  such  as  would  prevail  in  careful  commercial 
work : 

TABLE    I.— LOSSES  OF  GOLD  AND  SILVER  IN  CUPELLATION. 


Wt.  Silver 
before 

Cupelling. 

Wt.  Gold 
before 
Cupelling. 

Wt.  Silver 
after 
Cupelling. 

Wt.  Gold 
after 
Cupelling. 

Silver 
Loss. 

Gold  Loss. 

Silver 
Loss 
Per  Cent. 

Gold  Loss 
Per  Cent. 

210.765 

338.030 

206.360 

335.025 

4405 

3-005 

2.09 

0.888 

543-I65 

349-020 

535.645 

348.200 

7.520 

0.820 

1.38 

0.234 

206.360 

335.025 

200.325 

334.365 

6.035 

0.660 

2.92 

0.197 

535.645 

348.200 

523.330 

346.900 

12.315 

1.300 

2.29 

0-373 

200.325 

334.365 

196.720 

333.120 

3.905 

1.245 

1.79 

0.372 

523.330 

346.900 

514.765 

345.790 

8.565 

i.  no 

1.63 

0.319 

196.720 

332.575 

191.733 

33L725 

4.987 

0.850 

2.53 

0.255 

5M.765 

345.790 

503.950 

344.150 

10.815 

1.640 

2.10 

0-474 

I9I-735 

331.725 

187.820 

330.600 

3013 

1.125 

2.03 

0-33& 

434-lSo 

344.965 

424.925 

344.265 

9-255 

0.700 

2.13 

O.2O2 

187.820 

330.600 

184.525 

329.900 

3.295 

0.700 

1.  80 

0.2II 

424.925 

334.650 

419.975 

333.960 

4-050 

0.690 

0-95 

0.206 

184.525 

329.900 

180.560 

329.130 

3.965 

0.770 

2.14 

0.233 

419-975 

220.635 

410.430 

220.200 

9-545 

0-435 

2.27 

0.197 

410.430 

329.130 

403.365 

328.860 

7-075 

0.270 

1.72 

0.082 

403  365 

220.200 

394-550 

2I9.835 

8.815 

0.365 

2.18 

0.165 

Average  silver  loss 1.99  per  cent.        Average  gold  loss 0.296  per  cent. 


APPENDIX   C. 


389 


The  following  table  gives  the  results  of  some  experiments 
undertaken  by  the  author  to  determine  the  losses  under 
various  conditions : 


TABLE  II.— LOSS  OF  GOLD  IN  CUPELLATION. 


No. 

Parts 
Gold 
Taken. 

Parts 
Silver 
Taken. 

Grms. 
Lead 
Taken 

Parts  Ag 
and  Au 
after 
Cupella- 
tion. 

Parts  Au 
after 
Parting. 

Parts  Ag. 

Loss  Au 
Per  Cent. 

LossAg 
Per  Cent. 

Ai 

799-8 

.... 

7 

795-4 

.... 

.... 

0-55 

2 

799.8 

.... 

7 

795-0 

.... 

O.6o 

3 

799-8 

.... 

7 

795-0 

.... 

.... 

O.6o 

4 

800.3 

.... 

7 

794-8 

.... 

.... 

0.69 

5 

799-9 

.... 

7 

795-7 

.... 

.... 

0.52 

6 

799-9 

.... 

7 

798.0 

.... 

.... 

0.23 

Bi 

200.7 

.... 

4 

194.4 

.... 

.... 

3-i* 

2 

200.8 

.... 

4 

194.6 

.... 

.... 

3-09 

3 

2OO.6 

.... 

4 

195.3 



.... 

2.64 

4  i     200.4 

.... 

4 

197-3 

.... 

.... 

i-55 

5 

200.4 

.... 

4 

199.1 

.... 

.... 

0.65 

C  i 

200.1 

.... 

8 

192.4 

.... 

.... 

3-85 

2 

2OO.O 

.... 

8 

191.4 

.... 

.... 

4-30 

3 

200.1 

.... 

8 

193-7 

.... 

.... 

3-20 

4 

200.0 

.... 

8 

196.2 

.... 

.... 

1.90 

5 

200.6 

.... 

8 

1.99.4 

.... 

.... 

0.60 

Di 

800.0 

2OO.2 

7 

987.7 

.... 

.... 

1.23 

} 

2 

3 
4 

799.8 
799-8 

799-8 

199.7 
199.6 
2OO.O 

7 
7 
7 

987.7 
989.0 
989.0 

.... 



1.18 
1.04 
1.08 

Loss 
I  Agand 
f  Au  per 
cent. 

5 

799-9 

199.7 

7 

994.2 

.... 

.... 

0.52 

J 

Ei 

2OO.  2 

1000.6 

7 

1173.6 

2OO.2 

973-4 

o.oo 

2.75 

2 

200.1 

1000.8 

7 

H77.5 

2OO-4 

977-1 

*o.i5 

2-34 

3 

200.7 

IOOI.2 

7 

1185.4 

201.4 

984.0 

*o.35 

1.65 

4 

2OO.O 

1001.4 

7 

1190.9 

200.0 

990.9 

0.00 

1.05 

Fi 

100.35 

IOOO.O 

7 

.... 

100.35 

.... 

o.oo 

2 

100.35 

IOOO.O 

7 

.... 

IOO.25 

.... 

0.09 

3 

IOO-9 

IOOO.O 

7 

.... 

100.45 

.... 

0.44 

4 

IOO.4 

IOOO.O 

7 

.     .     .      3 

100.25 

.... 

0.15 

Gi 

IOI.9 

IOOO.O 

7 

.... 

IOI.7 

.... 

0.19 

2 

102.2 

IOOO.O 

7 

.... 

102.4 

*o.ig 

3 

IOI-5 

1000.0 

7 

.... 

IOI.I 

.... 

0.39 

4 

102.0 

IOOO.O 

7 

.... 

102.2 

.... 

*o.  19 

Hi 

100.6 

IOOO.O 

7 

.... 

99-3 

.... 

1.29 

2 

IOO.O 

IOOO.O 

7 

.... 

99.8 

.... 

0.20 

3 

100.  1 

IOOO.O 

7 

.... 

100.8 

.... 

*o.6g 

4 

100.3 

IOOO.O 

7 

.... 

100.5 

*o.ig 

5 

IOO.O 

IOOO.O 

7 

.... 

100.9 

.... 

*o.go 

Average  loss  Au  per  cent,  0.86.     *  Indicates  a  gain  in  place  of  loss. 


39°  APPENDIX   C. 

REMARKS. 

A.  No.  I  was  cupelled  at  the  back  of  the  muffle,  the  others 
being  placed  in  order  up  to  No.  6,  which  was  at  the  front. 
The  temperature  was  lower  than  is  usually  employed. 

B.  No.  i  run  at  the  rear  and  No.  5  in  front  of  the  muffle. 
The  temperature  was  higher  than  in  A. 

C.  The  conditions  were  the  same  as  in  B. 

D.  The  conditions  were  the  same  as  in  A. 

E.  The  conditions  were  the  same  as  in  B.     In  parting  but 
one  acid  (sp.  gr.  1.15)  was  used. 

F.  No.  i  at  the  rear  and  No.  4  in  the  front  of  the  muffle. 
The  temperature  was  higher  than  is  usual  in  commercial  work. 
The  parting  was  performed  in  two  acids  of  1.07  and    1.27  sp. 
gr.  respectively. 

G.  The  conditions  were  the  same  as  in  F,  except  that  the 
first  acid  was  1.20  and  the  second  acid  1.27  sp.  gr. 

H.  The  conditions  were  the  same  as  in  F,  except  that  in 
parting  but  one  acid  (sp.  gr.  1.15)  was  used. 

Table  III  gives  the  results  of  some  experiments  made  by 
the  author  to  determine  the  losses  under  various  conditions 
and  where  larger  amounts  of  lead  were  present.  Each  part  is 
0.5  milligramme. 

REMARKS. 

A.  No    i  was  cupelled  in  the  front  and  No.  2  in  the  middle 
of  a  hot  muffle. 

B.  Nos.  i  and  2  in  the  front  and  Nos.  3  and  4  in  the  middle; 
300  parts  of  copper  were  added. 

C.  No.  i   in  front  and  No.  2  in  the  middle ;  600  parts  of 
copper  were  added. 

D.  Nos.  i   and  2  in  front  and  No.  3  in   the   middle  ;  600 
parts  of  zinc  were  added. 

E.  Nos.  i  and  2  in  front  and  Nos.  3  and  4  in  the  middle ; 
350  parts  of  zinc  and  300  parts  of  antimony  were  added. 

F.  No.  i   in  front  and  No.  2  in  the  middle  ;  200  parts  of 
copper,  250  parts  of  zinc,  200  parts  of  antimony,  and  200  parts 
of  iron  sulphide  were  added. 


APPENDIX   C.  3QI 

TABLE  III.— LOSSES  OF  GOLD  AND  SILVER  IN  CUPELLATION. 


No. 

Parts 
Au 
Taken  . 

Parts 
Ta^ln. 

Grammes 
Pb 

Taken. 

Parts  Ag 
and  Au 
after 
Cupella- 
tion. 

Parts  Au 
after 
Parting. 

Parts 
Ag. 

Loss 
Au 
Per  Cent. 

Loss 
Ag 
Per 

Cent. 

Ai 

3-6 

3OO.6 

14-5 

295.8 

3-4 

292.4 

2-55 

2.67 

2 

355 

301.0 

14-5 

282.6 

3-4 

279.2 

4-25 

7-24 

Bi 

3-5 

300.6 

14.4 

296.5 

3-3 

293-2 

5-71 

2.46 

2 

3-o 

300.7 

14.4 

296.9 

2.9 

294.0 

3.33 

2.23 

3 

3-7 

3OO.2 

14.4 

280.6 

3-4 

277.2 

8.  ii 

7.66 

4 

3-45 

300.3 

14.4 

281.6 

3.05 

278.5 

H-59 

7.26 

C  i 

4-3 

300.5 

14.2 

297.8 

4.2 

293-6 

2.32 

2.23 

2 

4.1 

300.4 

14.2 

278.8 

4.0 

274.8 

2.50 

8.52 

Di 

3-8 

300.7 

14.2 

290.1 

3-5 

286.6 

7-9° 

4.68 

2 

3-7 

300.0 

14.2 

288.5 

3-4 

285.1 

8.10 

4.96 

3 

3-5 

300.5 

14.2 

271.0 

3-35 

267.6 

4-30 

10.94 

Ei 

3-6 

3OO.O 

14. 

287.6 

3-3 

284.3 

8-33 

5-23 

2 

3-0 

300.0 

14. 

288.1 

2-7 

285.4 

IO.OO 

487 

3 

4.2 

300.2 

14. 

275-7 

3-8 

271.9 

9-52 

9-43 

4 

3-2 

300.6 

14. 

270.2 

2.8 

267.4 

12.  8l 

14-37 

Fi 

4.2 

300.0 

14. 

291.4 

3-9 

287.5 

7.14 

4.17 

2 

4.2 

301.8 

14. 

279-5 

4.1 

275-4 

2.38 

8-74 

Gi 

8.7 

331.0 

14-5 

334-8 

8.65 

326.15 

0.57 

1.46* 

2 

5-15 

340.8 

14-5 

340.6 

5-05 

335-55 

1.94 

1-54* 

3 

5-i 

326.9 

14-5 

326.8 

5-oo 

321.8 

1.96 

1.56* 

4 

5-5 

334-7 

14.5 

334-7 

5-40 

329-3 

1.82 

1.61* 

J  i 

3-4 

3I7.I 

14.5 

314.4 

3-37 

311-03 

0.90 

1.92* 

2 

3-6 

332.65 

14-5 

327.2 

3-56 

323-64 

i.  ii 

2.71* 

Ki 

4.8 

332-4 

14.4 

3260 

4-65 

321.35 

3-12 

3-32 

2 

4.4 

349-6 

14.4 

339-8 

4.2 

335.6 

4.54 

4.00 

Li 

3-9 

314.6 

14.4 

308.9 

3-7 

305.2 

5.13 

2.98 

2 

3-7 

315.8 

14.4 

3H-4 

3-5 

307-9 

5.40 

2.50 

Ml 

3-95 

302.0 

14.2 

290.9 

3-72 

286.18 

5.82 

5-23 

2 

3-2 

306.9 

14.2 

296.3 

3-00 

293-3 

6.25 

4-43 

Ni 

3.6 

300.0 

14. 

292.4 

3-55 

288.85 

1.30 

3-71 

2 

3-3 

312.0 

14. 

306.9 

3-25 

303-65 

1.51 

2.68 

In  all  of  the  above  cases  the  buttons  were  cupelled  at  too 
high  a  temperature  to  show  feather-litharge  on  the  cupel. 

In  the  following  experiments  the  cupellations  were  all  per- 
formed in  the  front  of  the  furnace  and  all  the  cupels  showed 
litharge  crystals. 

G.*  The  gold  and  silver  were  wrapped  in  pure  lead  and 
cupelled  cold.  The  average  loss  in  silver  was  1.54  per  cent, 
and  in  gold  1.32  per  cent.  These  results  agree  closely  with  a 
number  of  results  previously  obtained  by  the  author  in  the 


392  APPENDIX   C. 

cupellation  of  base  bullion  from  silver-lead  blast-furnace 
smelting. 

In  the  following  experiments  the  charges  were  scorified 
previous  to  cupellation,  the  buttons  after  scorification  weighing 
from  5  to  6  grammes.  The  results  confirm  the  author's  pre- 
vious experience  in  operating  on  base  bullion,  there  being  no 
advantage  in  previous  scorification  except  in  the  case  of  ex- 
tremely base  bullion.  Even  in  the  case  of  quite  impure  bull- 
ion, provided  the  cupellations  are  started  hot  and  as  soon  as 
the  lead  begins  to  drive  well,  if  the  cupels  are  moved  forward 
so  that  the  cupellations  are  continued  cold  the  results  will  be 
quite  as  high  as  where  previous  cupellation  is  adopted. 

J.   14.5  grammes  of  pure  lead  were  used. 

K.  300  parts  of  copper  were  added. 

L.  400  parts  of  zinc  were  added. 

M.  300  parts  of  zinc  and  300  parts  of  copper  were  added. 

N.  300  parts  of  zinc,  250  parts  of  copper,  300  parts  of  anti- 
mony, and  350  parts  of  iron  sulphide  were  added. 

Table  IV  gives  the  results  of  Messrs.  Mason  and  Bowman's 
experiments  to  determine  the  losses  in  scorification  and  cupel- 
lation. 

In  Table  I  we  found  the  loss  of  silver  in  cupellation  to  be 
1.99  per  cent.,  and  the  loss  in  gold  in  cupellation  to  be  0.296 
per  cent.  Deducting  these  percentages  from  the  above  aver- 
ages (Table  IV),  we  have  for  the  losses  in  scorification  :  Silver 
0.55  per  cent.,  and  gold  0.574  per  cent. 

Table  V  gives  the  results  of  Mr.  Henry  E.  Wood,  assayer, 
Denver,  Colo.,  on  the  assay  of  silver  sulphides  by  scorification 
and  cupellation.  In  these  experiments  the  slags  and  cupels 
were  saved,  and  the  absorbed  silver  subsequently  determined. 
They  do  not  show  the  silver  lost  by  volatilization. 

Table  VI  (Frederic  P.  Dewey)  gives  the  results  on 
eleven  lots  of  regular  Russell  process  sulphides  assayed  as 
follows :  Weigh  out  -fa  A.  T.  of  sulphides,  55  gms.  of  test-lead, 
and  2  or  3  gms.  of  borax-glass.  One  half  of  the  test-lead  is 
placed  in  the  bottom  of  the  scorifier  and  hollowed  out ;  the 
sulphides  are  put  into  the  hollow  and  the  balance  of  the  test- 


APPENDIX   C. 


393 


TABLE  IV.— LOSSES   OF    GOLD    AND    SILVER  IN  SCORIF1CATION 
AND  CUPELLATION. 


Wt.  Silver 
before  Scori- 
fying and 
Cupelling. 

Wt.  Gold 
before  Scori- 
fying and 
Cupelling. 

Wt.  Silver 
after  Scori- 
ging  and 
upelling. 

Wt.  Gold 
after  Scori- 
fying and 
Cupelling. 

Silver 
Loss. 

Gold 
Loss. 

Silver 
Loss, 
Per 
Cent. 

Gold 
Loss, 
Per 
Cent. 

466.850 

357-750 

453.200 

35L982 

13.650 

5.768 

2.92 

1.  6l 

480.052 

388.525 

469o75 

382.565 

10.477 

5.960 

2.18 

1-53 

455-000 

353.782 

434.365 

346.234 

20.635 

7.548 

4-53 

2.10 

471-375 

384-365 

456.475 

382.033 

14.900 

2.332 

3  16 

O.6O 

436.165 

348.034 

425.780 

346.325 

10.385 

1.709 

2.38 

0.49 

458.275 

383.833 

448.818 

381.875 

9-457 

1.958 

2.06 

0.51 

427-580 

348.125 

418.533 

346.435 

9-057 

1.690 

2.II 

0.48 

652.350 

478.120 

641.520 

471.920 

10.830 

6.2OO 

1.66 

1.29 

354.200 

348.235 

344-520 

346.250 

9.680 

1.985 

2.73 

o.57 

643.320 

473-720 

628.175 

471.225 

15.155 

2.495 

2-35 

0.52 

346.320 

348.050 

340.500 

346.465 

5.820 

1.585 

1.68 

0-45 

614.920 

356.425 

600.565 

352.435 

14-355 

3.990 

2.33 

i.  ii 

342.300 

348.265 

333.075 

345-535 

9.225 

2.730 

2.69 

0.78 

602.365 

354.235 

592.200 

352.525 

10.165 

1.710 

1.68 

0.48 

334-875 

347-335 

327.140 

345.800 

7.735 

1.535 

2.30 

0.44 

5  94-  coo 

354.325 

581.465 

352.075 

12.535 

2.250 

2.  II 

0.63 

328.840 

347.600 

317.830 

344-135 

II.  HO 

3.465 

3-37 

0  99 

567.620 

353-875 

555.365 

350.925 

12.535 

2.950 

2.15 

0.83 

219.450 

221.635 

210.765 

219.250 

8.685 

2.385 

3-95 

1.07 

557.165 

352.725 

543.165 

349-020 

14.000 

3.705 

2.51 

1.05 

Average  silver  loss.  .  .  .  2.54  per  cent.         Average  gold  loss. .  . .  0.87  per  cent. 

lead  poured  over  them  ;  the  borax  is  then  placed  on  top.  The 
assay  is  then  conducted  in  the  usual  manner,  the  slags  and 
cupels  being  saved,  ground  up,  and  assayed,  the  result  being 
added  to  the  regular  assay. 

Table  VII  gives  the  results  of  a  number  of  experiments 
undertaken  by  the  author  to  determine  the  loss  of  silver  in  the 
assay  of  rich  silver  sulphides,  and  also  to  see  if  some  method 
other  than  the  foregoing  might  not  be  adopted  to  advantage. 

A  few  ounces  of  silver  sulphide  were  prepared  by  dissolv- 
ing quite  pure  silver  chloride  in  sodium  hyposulphite  and  pre- 
cipitating the  silver  as  a  sulphide  by  the  addition  of  sodium 
sulphide  to  the  solution.  After  filtration  and  slight  washing, 
the  precipitate  was  dried,  ground,  and  thoroughly  mixed ;  and 
the  percentage  of  silver  was  then  determined  by  carefully 


394 


APPENDIX   C. 


TABLE  V.— LOSSES   IN   THE  SCORIFICATION-ASSAY    OF  SILVER 

SULPHIDES. 


Ounces  of  Silver 
per  Ton  of 
Sulphides. 

Average  of 

Per  Cent.  Silver  Recovered 
from 
Slag  and  Cupel. 

Under  500 

i  lot 

4.170 

500  to     1,000 

6  lots 

2.910 

1,000  to     1,500 

14  lots 

2.996 

1,500  to     2,000 

9  lots 

2.540 

2,000   tO      2,500 

12  lots 

2.109 

2,500  to     3,000 

21  lots 

.867 

3,000  to     3,500 

19  lots 

.860 

3,500  to     4,000 

19  lots 

.821 

4,000  to     4,500 

10  lots 

.695 

4,500  to     5,000 

7  lots 

.700 

5,000  to     5,500 

4  lots 

.845 

5,500  to    6,000 

4  lots 

.895 

6,000  to    6,500 

I  lot 

.630 

6,500  to     7,000 

4  lots 

•777 

7,000  to     7,500 

2    lots 

.640          / 

7,500  to     8,000 

I  lot 

.420 

8,000  to     8,500 

3  lots 

•  537 

9,000  to     9,500 

3  lots 

.460 

10,500  to  11,000 

i  lot 

•570 

11,500  to  12,000 

i  lot 

•340 

12,000   tO    12,500 

i  lot 

.270 

17,000  to  17,500 

i  lot 

.260 

weighing  out  several  portions  of  0.05  A.  T.*  each  on  the  assay- 
balance  used  for  weighing  the  silver  buttons  resulting  from 
assays ;  dissolving  each  portion  in  nitric  acid  of  27°  Baume ; 
boiling  to  expel  the  red  fumes ;  diluting  with  distilled  water  to 
200  cc.,  and  titrating  with  a  standard  solution  of  potassium 
sulphocyanate ;  adding  about  i  cc.  of  a  strong  solution  of 
ammonium  ferric  alum  as  an  indicator  (Volhard's  method). 
This  method  was  adopted  because  the  Gay-Lussac  titration 
with  standard  salt  solution  could  not  be  used  on  account  of 
the  sulphur  set  free  during  solution  and  the  consequent  cloudi- 
ness of  the  solution.  This  free  sulphur  would  also  have  inter- 
fered with  the  gravimetric  determination  (precipitating  the 

*  The  result  have  been  reduced  to  ounces  per  ton,  rather  than  percent- 
ages, for  the  sake  of  uniformity  and  convenience.  One  ounce  per  ton  is 
0.00343  per  cent. 


APPENDIX   C. 


395 


TABLE  VI.— LOSSES    IN   THE   SCORIFICATION-ASSAY   OF  SILVER 

SULPHIDES. 


Oz.  per  Ton  by 
Commercial 

Oz.  per  Ton 

in 

Per  Cent, 
in 

Total  Oz.  per  Ton. 

Total  Oz.  per 

Assay, 
ist  Assayer. 

Slag  and  Cupel, 
ist  Assayer. 

Slag  and  Cupel, 
ist  Assayer. 

ist  Assayer. 

Ton. 
ad  Assayer. 

8,675.20 

144.11 

.622 

8,819.31 

8,782 

10,074.25 

18935 

.844 

10,263.60 

10,119 

10,783.35 

189.00 

.720 

10,972.35 

10,938 

10,902.30 

194.38 

•  752 

11,096.68 

II,22O 

11,015-73 

191.69 

.710 

11,207.42 

II,O9O 

11,238.40 

175-2?. 

.535 

II,4I3-62 

H,548 

11,828.75 

176.72 

.471 

12,005.47 

12,046 

12,566.55 

199.21 

.560 

12,765.76 

12,821 

12,665.85 

199.87 

•  553 

12,865.72 

12,841 

13,001.65 

229.84 

•737 

13,231.49 

13,187 

13,625  50 

226.52 

.635 

13,852.02 

13,919 

silver  as  a  chloride  and  weighing  it  as  such).  Volhard's 
method,  provided  copper  is  absent,  gives  very  correct  results, 
and  has  been  used  by  the  writer  for  years  with  entire  satisfac- 
tion. The  average  silver-contents  of  the  sulphides,  as  thus 
shown  by  several  closely-agreeing  determinations,  was  19,693 
ounces  per  ton  of  2000  pounds. 

The  silver  was  next  determined  by  the  combination  method 
described  in  Part  III,  Chapter  IV,  page  250.  The  result  of 
two  determinations  was  19,590  and  19,625  ounces  per  ton ; 
average,  19,608;  average  per  cent,  of  the  silver  present  thus 
found,  99.56. 

Table  VII  gives  the  results  of  the  different  determinations 
by  both  scorification-  and  crucible-assay. 

Remarks  on  the  Scorification- Assays. — The  assays  were  run 
in  the  usual  manner,  from  30  to  40  grammes  of  test-lead  and 
from  0.5  to  I  gramme  of  borax-glass  being  used.  In  addition 
to  the  regular  fluxes,  there  were  added  the  following  reagents : 

No.  i.  Grammes :  0.5  of  Sb2O4,  0.5  of  As2O5,  and  0.5  of  Cu. 
The  button,  after  cupellation,  weighed  19,764  milligrammes ; 
but,  as  it  showed  the  presence  of  copper,  it  was  recupelled  with 
i  gramme  of  lead,  and  the  weight  of  this  second  button  is  the 
result  reported  in  the  table. 


396 


APPENDIX   C. 


TABLE  VII.— COMPARISON  OF  SCORIFICATION-  AND  CRUCIBLE- 
ASSAYS. 


SCORIFICATION  METHOD. 

CRUCIBLE  METHOD. 

No. 

Amount  Sul- 
phides Taken. 

Result 
Ounces 
per  Ton. 

Result 
Percent, 
of  Ag 
Present. 

No. 

Amount 
Sulphides 
Taken. 

Grammes. 
0.5 
0-5 
05 
0.25 

0-5 
0.5 
0-5 
0-5 

Result 
Ounces 
per  Ton. 

Result 
Per  cento 
of  Ag 
Present. 

I 

0.05  A.  T. 
0.05 
0.05 
0.05 
0.05 
0.5  gramme. 
0'5 
0.5 

19.576 
19,714 
19062 
19.573 
I9.675 
19-547 
19,406 
19,611 

99.41 
100.  II 
99-33 
99-40 
99.91 
99-25 
98.54 
99-58 

I  

I9.556 
19,446 
19.501 
19,200 
18,734 
19,396 
19,416 
19,506 

99.20 
98.74 
99.02 
97-49 
95-13 
98.49 
98.59 
99-05 

<2 

2  

c    . 

6 

6  

7.  . 

7.  . 

s  

8  

Average 

Average. 

I9.583 

99-44 

19,344 

98.22 

No.  2.  The  charge  was  the  same  as  in  No.  i.  The  button 
weighed  19,841  milligrammes,  and  was  dissolved  in  nitric  acid, 
the  solution  showing  the  presence  of  copper.  The  result,  as 
reported  in  the  table,  was  obtained  by  titration  of  the  solution 
from  the  button  with  standard  sulphocyanate  solution,  which 
method  would  necessarily  give  a  high  result,  owing  to  the 
presence  of  copper. 

No.  3.  This  was  run  without  the  addition  of  fluxes  other 
than  the  regular  charge  of  test-lead  and  borax. 

No.  4.  Same  as  No.  3. 

No.  5.  Added  grammes  :  BaSO4,  0.5  ;  SbaO4,  0.5  ;  FeS,  04 ; 
Cu,  0.5,  and  Zn,  0.5. 

No.  6.  Added  0.5  gramme  of  Cu. 

No.  7.  Added  0.5  gramme  of  Zn. 

No.  8.  Added  0.5  gramme  of  FeC. 

Remarks  on  the  Crucible-Assays. — The  fusions  were  run  in 
lO-gramme  Denver  crucibles,  the  fusion  being  performed  in  the 
muffle-furnace.  The  regular  charges  of  litharge,  sodium  bi- 
carbonate, borax-glass,  lead-flux,  and  nails  were  added.  The 
time  of  fusion  was  about  thirty  minutes  in  each  case.  In 


APPENDIX   C.  397 

addition  to  the  regular  fluxes  there  were  added  the  following 
reagents : 

No.  i.  Added  0.5  A.  T.  of  pure  SiO2. 

No.  2.  Added  grammes  :  SiO2,  5 ;  Sb2O4,  i ;  As2O6,  I ;  Cu, 
I,  and  S,  i. 

No.  3.  Added  0.5  A.  T.  of  pure  SiO2. 

No.  4.  The  same  as  No.  3. 

No.  5.  Added  grammes :  SiO2,  5  ;  BaSO4,  5  ;  Fe2O3,  5. 

No.  6.  Added  14  grammes  of  pure  SiO2. 

No.  7.  Added  grammes:  SiO2,  5  ;  Zn,  I  ;  S,  I,  and  Cu,  0.5. 

No.  8.  Added  grammes :  SiO2,  5  ;  BaSO4,  5,  and  Fe2O3,  5. 

In  all  the  assays  the  same  precautions  were  adopted  as 
would  ordinarily  be  observed  in  careful  commercial  work. 

The  crucible-assays  were  made,  not  because  this  was  con- 
sidered the  proper  method  for  the  assay  of  high-grade  silver 
sulphides,  but  in  order  to  obtain  comparative  results  by  this 
and  the  scorification  method. 

The  following  table  gives  the  results  of  a  few  experiments 
undertaken  by  the  author  to  determine  the  loss  of  gold  and 
silver  in  the  crucible-assay  of  ores.  Whilst  the  results  show 
too  great  a  variation  for  any  averages  to  be  derived  from 
them,  they  tend  to  show  that  the  crucible-assay  for  gold  is  more 
accurate  than  is  generally  supposed.  The  average  loss  in 
silver  (2.58  per  cent.)  in  these  experiments  is  quite  close  to 
that  found  by  Mason  and  Bowman  in  the  scorification-assay 
(2.54  per  cent.). 

REMARKS. 

A.  £  A.  T.  of  pure  SiO2  was  added. 

B.  10   grammes   of   SiO2   and    5    grammes  of   ZnO  were 
added. 

C.  £  A.  T.  SiO2  added.     The  button  was  not  weighed  prior 
to  parting. 

D.  £  A.  T.  of  SiO2  was  added.     No  silver  was  added  to 
this  assay. 


APPENDIX  .C. 
TABLE  VIII.—  LOSSES  OF  GOLD  AND  SILVER  IN  CRUCIBLE-ASSAY. 


No. 

Parts  Au 
Taken. 

Parts  Ag 
Taken. 

Parts  Au 
and  Ag 
after 
Cupellation. 

Parts  Au 
after 
Parting. 

Parts  Ag. 

Loss  Au 
Per  cent. 

Loss  Ag 
Per  cent. 

Ai 

2 

Bi 

2 

r 

4-7 
4.0 
4.0 

3-6 
202  5 

216.3 

205-5 
2O8.O 
217.6 
2OOO 

215.6 
206.5 
208.7 
217.2 

4.65 
4.0 
4.0 
3.6 
202  6 

210.95 

202.5 

204.7 
213.6 

1.  06 
0.00 

o.oo 
o.oo 

+    O  O.1 

2-47 
1.93 
1.58 
1.84 

n 

200  8 

2OO    3 

o  28 

*    *    *    * 

E  i 

2 

F  i 

2 

G 

Hi 

2 

K 

24.25 
24.6 
26.4 
22.3 
13-4 
14-5 
15-3 
14.4 

306.0 

317.5 
320.7 
308.9 
226.8 
215.2 
214.9 
232.0 

32I.O 
330.1 
340-4 
324-0 
235-3 
225.8 
223.0 
235-4 

24-23 

24-5 
26.4 
22.3 
13-3 
14.5 
15-2 
14.25 

296.77 
305-6 
314.0 
300.7 
222.  0 
2II.3 
207.8 
221.15 

Average.  . 

0.08 
0.40 

0.00 

o.oo 
o  74 

0.00 

0.65 
1.04 

o  ^o 

3-oi 
3-74 
2.08 
2.65 

2.  II 

1.81 
3-30 
4.66 
2  t;8 

E.  5  grammes  of  SiOa,  5  grammes  of  BaSO4  and  5  grammes 
of  FeS  were  added. 

F.  10  grammes  of  FeS,  3  grammes  of  ZnO  and  2  grammes 
of  Cu  were  added. 

G.  7.5   grammes  of  SiO2  and  5   grammes  of  BaSO4  were 
added. 

H.  5  grammes  of  SiOa,  5  grammes  of  BaSO4and5  grammes 
of  CaO  were  added. 

K.  7.5  grammes  of  SiO2  and  7  grammes  of  FeS  were  added. 

To  the  above  charges  there  were  added  the  proper  fluxes 
to  produce  a  fluid  slag  and  a  lead  button  of  from  7  to  12 
grammes  in  weight.  The  cupellations  were  performed  so  as 
to  show  "  feather-litharge  "  on  the  cupels  in  each  case.  The 
parting  was  done  in  two  acids  of  1.15  sp.  gr.  and  1.27  sp.  gr. 
respectively. 

In  connection  with  Table  VIII  the  following  results  re- 
cently obtained  by  the  author  on  some  samples  of  Cripple 
Creek  telluride  ores  will  be  of  interest.  The  gold  was  deter- 
mined independently  by  an  eminent  chemist  by  wet  analysis. 
The  fire-assays  were  made  by  the  author : 


APPENDIX   C.  399 

TABLE  IX.— COMPARISON  OF  WET  AND  FIRE  ASSAYS  FOR  GOLD. 


Sample 

No. 

Oz.  Au 
by  Wet 

Metnod. 

Oz.  Au 
by  Crucible 

Method. 

Oz.  Au  by 
Scorification 
Method. 

I.  ... 

qn  o 

•3Q     O 

<JQ       C 

2  

Q.O 

39-5 
8.8 

39-0 
8  8 

21.8 

9.0 

22    ^ 

9.0 

21    2 

22.0 

21.8 

For  the  scorification-assays  -^  A,  T.  of  the  ore  was  taken 
in  the  case  of  samples  Nos.  i  and  3.  In  the  case  of  No.  2  -fa 
A.  T.  was  taken.  The  charge  in  each  case  was :  test-lead.  40 
grammes  ;  litharge,  10  grammes,  and  borax-glass,  0.5  grammes. 
The  ore  was  mixed  with  one  half  of  the  test-lead.  The  lith- 
arge was  then  added  as  a  cover,  and  on  top  of  this  was  placed 
the  remainder  of  the  test-lead  and  the  borax. 

For  *the  crucible-assays  the  following  charge  was  used: 

Ore ^  A.  T. 

Litharge. . .  , 50  grammes 

Lead  flux 6 

Soda  bicarb. 5         " 

Borax -glass 3         " 

Nail  ...„ One. 

Whilst  this  table  would  seem  to  conflict  with  those  preced- 
ing it,  which  have  shown  that  there  is  a  considerable  loss  of 
gold  in  fusion,  etc.,  it  must  be  remembered  that  there  is  also 
always  some  silver  left  with  the  gold  after  parting.  Where 
the  parting  is  properly  performed  this  gain  will  frequently 
nearly  equal  the  loss  of  gold  in  the  previous  operations.  A 
recent  analysis  of  a  quantity  of  gold  resulting  from  careful 
parting  showed  it  to  contain  0.3  per  cent,  of  silver.  An  analy- 
sis of  some  gold  resulting  from  parting  where  only  one  dilute 
acid  had  been  used  showed  it  to  contain  1.15  per  cent,  of 
silver. 


4OO 


APPENDIX   C. 


The  following  table  gives  the  results  of  a  number  of  experi- 
ments made  by  T.  K.  Rose*  to  determine  the  loss  of  gold  in 
the  assay  of  gold  bullion. 

TABLE  X.— LOSS   OF  GOLD    IN  THE  ASSAY    OF    GOLD    BULLION. 


Standard  of  Alloy. 

Surcharge  on  the 
Assay  Piece. 

Loss  of  Gold  per  1000 
of  Pure  Gold. 

916.6 

+0.250 

0.63 

900.0 

+0.225 

0.65 

800.0 

-0.075 

1.  00 

666.6 

—  0.2 

1.  20 

546.0 

-0.7 

2.20 

333-3 

-2.8 

9-30 

Prof.  Roberts-Austenf  found  the  loss  of  gold  to  be  0.723 
at  the  ordinary  temperature,  and  0.645  at  a  slightly  lower 
temperature  than  is  usual  in  gold  bullion  assaying,  using  Brit- 
ish standard  gold  (916.6  parts  gold  and  83.4  parts  copper). 

*  The  Metallurgy  of  Gold.     T.  Kirke  Rose.     London,  1894 
f  Percy's  Metallurgy  of  Silver  and  Gold,  p.  275. 


APPENDIX  D. 


LABORATORY  TESTS  IN  CONNECTION  WITH  THE 
EXTRACTION  OF  GOLD  FROM  ORES  BY  THE 
CYANIDE  PROCESS. 

As  the  cyanide  method  for  the  extraction  ot  gold  from 
ores  is  extensively  used  in  the  United  States  and  elsewhere, 
and  appears  destined  to  prove  a  factor  of  increasing  impor- 
tance in  the  metallurgy  of  gold,  a  description  of  the  latest 
laboratory  methods  may  prove  of  interest. 

The  history  of  the  development  of  the  process  in  the 
United  States  has  been  analogous  to  that  of  all  new  processes. 
Many  failures  are  to  be  recorded  and  a  few  successes.  It  is 
the  opinion  of  the  writer  that,  had  the  following  simple  tests 
been  better  understood,  many  of  the  failures  would  not  have 
occurred,  and  we  should  probably  have  a  larger  number  of 
successful  plants  in  operation.  While  the  process  is  not 
simple,  but  requires  a  high  degree  of  chemical  and  engineer- 
ing skill,  the  determination  of  the  adaptability  of  an  ore  to 
the  method  is  generally  not  difficult.  While  the  laboratory 
results  will  not  always  coincide  with  the  actual  results 
obtained  in  the  mill,  they  will  serve  as  a  guide  and  control  on 
the  working  of  the  mill,  and  will  generally  suffice  to  determine 
if  the  ore  can  be  economically  treated  by  the  process.  Objec- 
tion may  reasonably  be  made  that  in  small  tests  conditions 
different  from  those  which  occur  on  a  larger  scale  are  intro- 
duced. However,  tests  made  on  from  25  to  100  pounds  of 
ore  should  be  closely  duplicated  in  the  mill.  Tests  on  a 

401 


432  APPENDIX  D. 

smaller  scale  will  serve  to  show  what  may  be  expected  in  the 
mill. 

In  determining  the  adaptability  of  an  ore  to  this  method 
of  treatment,  and  the  percentage  of  extraction  which  may 
be  expected  in  the  mill,  the  following  must  receive  considera- 
tion: 

The  percentage  of  extraction  will  generally  be  somewhat 
higher  in  the  laboratory  than  in  the  mill,  but  the  consumption 
of  cyanide  will  also  be  higher  in  the  laboratory. 

'^A  most  important  point  is  the  character  of  the  ore,  par- 
ticularly the  manner  in  which  the  gold  is  contained  in  it; 
whether  it  is  in  the  free  state;  coarse  or  fine;  intimately 
associated  with  pyrites  or  other  sulphides;  the  character  of 
the  sulphides  with  which  it  is  associated;  whether  it  is  com- 
bined or  alloyed  with  bismuth,  tellurium,  or  other  elements. 
An  examination  by  the  eye,  with  or  without  the  aid  of  a  mag- 
nifying-glass,  will  frequently  settle  these  points.  Should  the 
sample  be  in  a  finely  pulverized  condition,  careful  vanning 
may  be  resorted  to  with  advantage. 

IXThe  size  to  which  it  is  advantageous  to  crush  the  ore  will 
depend  largely  upon  the  character  of  the  ore  and  its  gangue. 
Should  the  gold  be  unevenly  disseminated  throughout  the 
material,  and  the  gangue  be  hard  and  non-porous,  fine  crush- 
ing is  essential  to  a  good  extraction.  The  Cripple  Creek  ores 
are  examples  of  such  material,  crushing  to  4O-mesh,  or  finer, 
being  necessary  to  insure  a  good  extraction  of  the  gold. 
Some  ores,  however,  being  very  porous,  readily  permit  the 
solutions  to  percolate,  and  consequently  can  be  successfully 
leached  in  a  coarse  condition.  The  Mercur  ores  are  examples 
of  such  material,  pieces  one-half  inch  or  more  in  diameter 
being  successfully  leached. 

Whether  the  ore  requires  roasting  prior  to  leaching  will 
depend  principally  upon  the  condition  of  the  gold  in  it.  If 
present  as  a  telluride,  the  gold  may  be  extracted  from  the 
raw  ore  by  fine  grinding  and  leaching  with  potassium  cyanide; 
but  the  action  of  the  solution  on  the  tellurides  is  slow,  and  it 
may  be  more  economical  to  subject  the  ore  to  a  preliminary 


APPENDIX  D.  403 

roast.  Roasting  presents  two  disadvantages;  it  materially 
increases  the  cost  of  treatment,  and  it  is  liable  to  result  in 
the  formation  of  salts  detrimental  to  the  subsequent  leaching; 
for  example,  soluble  sulphates,  which  decompose  potassium 
•cyanide.  Unless  the  roasting  is  carefully  conducted,  gold 
may  be  lost  by  volatilization.  This  is  especially  the  case  with 
tellurides.  On  the  other  hand,  many  ores  are  rendered  more 
porous  by  roasting,  and  thus  the  rate  of  percolation  is  in- 
creased and  coarser  particles  can  be  leached. 

The  best  strength  of  solution  and  the  time  of  maceration 
and  percolation  are  important  points.  The  time  required  and 
the  amount  of  cyanide  consumed  will  depend  largely  upon  the 
strength  of  the  solution  employed.  For  example,  the  time 
required  with  a  I  per  cent  solution  will  generally  be  much  less 
than  with  an  0.25  per  cent  solution.  On  the  other  hand,  for 
many  ores  the  consumption  of  cyanide  with  a  I  per  cent  solu- 
tion is  so  great  that  the  process  becomes  commercially  im- 
practicable, while  with  dilute  solutions  the  ore  may  possibly 
be  treated  with  success.  In  this  connection  mention  may  be 
made  of  the  use  of  additional  reagents,  such  as  sodium  per- 
oxide, bromine,  etc.,  which  are  said  to  facilitate  the  extraction 
in  many  cases.  This  is  a  mooted  point,  and  the  use  of  these 
reagents  is  objected  to  by  some,  as  they  have  a  tendency  to 
increase  largely  the  consumption  of  zinc,  when  zinc  is  the 
precipitant  employed,  and  to  foul  the  solution.  According 
to  the  equation  of  Eisner, 

4Au  +  8KCN  +  O2  +  2H,O  =  4KAu(CN)2  +  <KOH, 

oxygen,  or  an  oxidtzer,  is  essential  to  the  solution  of  the  gold. 
It  would  appear  to  the  writer  that  the  necessary  oxygen  can 
be  obtained  from  the  air  at  less  cost,  and  quite  as  conveniently, 
as  by  the  introduction  of  expensive  reagents. 

The  amount  of  potassium  cyanide  required  per  ton  of  ore, 
including  the  amount  which  is  destroyed  during  treatment,  is 
a  vital  point.  The  character  of  the  ore  and  its  associated 
minerals  will  determine  the  consumption  of  cyanide. 

The  rate  of  percolation  of  the  solution  through  the  ore  is 


404  APPENDIX  D. 

• 

a  question  of  some  importance.  It  would  appear  as  if  too 
much  had  been  made  of  this  point,  as  it  is  essential  that  the 
solution  should  remain  in  contact  with  the  ore  for  a  consider- 
able time  in  order  to  insure  a  good  extraction.  On  most 
ores  the  percolation  will  generally  be  quite  as  rapid  as  the 
necessary  time  of  contact  will  permit. 

A  small  quantity  of  the  ore  should  be  ground  to  3O-mesh,. 
which  is  a  suitable  degree  of  fineness  for  the  preliminary 
experiments.  A  sample  is  carefully  cut  out  of  this  prepared 
pulp,  ground  to  pass  loo-mesh,  and  assayed  for  gold  and 
silver  in  the  usual  manner. 

A  quantity  of  stock  solution,  containing  0.5  or  0.6  per 
cent  of  potassium  cyanide,  should  be  prepared.  As  this  so- 
lution is  liable  to  decomposition,  it  should  be  kept  in  a 
stoppered  bottle,  protected  from  the  air  and  sunlight,  and 
should  be  tested  from  time  to  time  according  to  Test  6. 

It  is  necessary  that  the  water  used  in  making  up  the  stock 
solution  should  be  quite  pure.  It  should  always  be  tested  for 
impurities,  for  should  it  contain  iron  salts,  magnesium  Sul- 
phate, salts  with  an  acid  reaction,  soluble  sulphides,  free 
carbonic  acid,  or  sulphuric  acid,  they  will  decompose  the 
potassium  cyanide. 

I.  Determination  of  Acidity. — Should  an  ore  be  acid,  the 
result  will  be  decomposition  of  potassium  cyanide  unless  this 
acidity  is  destroyed  before  the  cyanide  solution  is  added. 

Soluble  Acidity. — Agitate  10  grammes  of  the  pulp  for  10 
minutes  with  50  cc.  of  water;  filter,  and  test  the  filtrate  with 
litmus-paper  for  acidity.  Should  acidity  be  shown,  wash  the 
ore  until  the  washings  no  longer  give  an  acid  reaction  when 
tested  with  litmus-paper.  Now  titrate  the  total  filtrate  with 
decinormal  caustic-soda  solution,  until  the  neutral  point  is 
obtained,  using  litmus  as  an  indicator. 

Latent  Acidity. — Transfer  the  washed  ore  to  a  small  por- 
celain evaporating-dish;  cover  with  water;  add  a  measured 
excess  of  decinormal  caustic-soda  solution;  stir  and  titrate  the 
excess  of  soda  with  decinormal-acid  solution.  This  gives  the 
latent  acidity. 


APPENDIX  D.  405 

Total  Acidity. — The  sum  of  the  above  tests  gives  the  total 
acidity;  but  as  this  is  frequently  all  that  is  required,  it  may 
be  determined  as  follows:  Introduce  10  grammes  of  the  pulp 
into  a  stoppered  bottle  with  some  water;  add  a  measured 
•excess  of  the  caustic-soda  solution,  agitate  for  20  minutes,  and 
then  titrate  back  with  decinormal-acid  solution. 

The  soluble  acidity  is  due  to  salts  with  an  acid  reaction, 
such  as  ferrous  sulphate,  zinc  sulphate,  copper  sulphate,  etc., 
or  to  free  sulphuric  acid  from  the  decomposition  of  pyrites, 
tellurous  acid,  etc.  It  may  be  overcome  by  giving  the  ore  a 
preliminary  wash  with  water.  This  washing  is  followed  by 
treatment  with  a  weak  solution  of  caustic  soda  or  caustic  lime, 
which  neutralizes  the  latent  acidity  due  to  basic  salts.  The 
amount  of  alkali  necessary  is  determined  from  the  quantity 
of  decinormal-soda  solution  used  in  the  above  experiments. 
Unless  the  ore  contains  a  large  amount  of  free  acid,  the  pre- 
liminary washing  with  water  may  be  omitted  ;  the  total  acidity 
being  determined  and  reported  in  terms  of  lime.  Sufficient 
lime  is  then  added  to  the  ore,  before  crushing,  so  that  it 
becomes  thoroughly  incorporated  before  the  ore  reaches  the 
tanks,  and  when  the  tank  is  charged,  the  cyanide  solution  is 
at  once  admitted. 

2.  Test  for  the  Consumption  of  Cyanide. — The  original 
strength  of  the  stock  solution  being  known,  it  is  only  neces- 
sary to  determine  its  strength  after  it  has  been  used  on  a  lot 
of  ore,  to  arrive  at  the  consumption. 

Introduce  20  grammes  of  ore  (treated  with  a  sufficient 
quantity  of  soda  or  lime,  if  necessary)  into  a  glass-stoppered 
bottle;  add  40  cc.  of  the  cyanide  solution,  and  agitate  for  20 
ininutes;  filter;  measure  off  20  cc.  of  the  filtrate  and  deter- 
mine the  amount  of  undecomposed  potassium  cyanide  remain- 
ing in  the  solution,  according  to  Test  6.  The  difference 
between  the  amount  of  potassium  cyanide  in  20  cc.  of  the 
stock  solution  and  the  quantity  found  above  gives  the  amount 
consumed  by  10  grammes  of  ore. 

If  the  consumption  of  cyanide  is  not  excessive  (which  will 
depend  altogether  on  the  value  of  the  ore,  as  rich  ores  can 


406  APPENDIX  D. 

stand  a  much  higher  consumption  than  those  of  lower  grade), 
or,  say,  not  over  4  pounds  of  potassium  cyanide  per  ton  of 
ore,  the  following  extraction  tests  can  be  proceeded  with. 

3.  Tests  for  the  Percentage  of  Extraction. — Generally 
two  series  of  tests  are  made — by  agitation  and  by  percolation. 

Agitation. — Take  four  4-ounce  wide-mouthed  glass-stop- 
pered bottles,  place  I  assay-ton  of  pulp  in  each,  then  add  to- 
each  60  cc.  of  solution  of  the  following  strength,  respectively : 
To  No.  i,  o.i  per  cent  KCN. 

"  2,  0.3          "  " 

"        3,  0.5        "  " 

"        4,  0.75      ". 

Before  adding  the  cyanide  solution,  the  proper  quantity  of 
neutralizer,  as  determined  in  Test  I,  is  added.  Allow  the 
bottles  to  stand  for  48  hours,  with  occasional  shaking.  Filter 
off  solutions;  wash  with  water  up  to  original  bulk;  test  an 
aliquot  portion  of  the  solution  for  loss  of  cyanide;  dry  the 
tailings;  crush  them  to  loo-mesh,  and  assay.  From  the 
assay  of  the  original  pulp  and  the  assay  of  the  tailings,  the 
percentage  of  extraction  can  be  calculated. 

Another  method  preferred  by  some  is  to  assay  the  tailings 
and  also  assay  the  solution  (see  Test  1 1);   then 
Percentage  of  extraction  = 

Assay  of  solution  X  Weight  of  solution  X  100 
(Assay  of  solution  X  Weight  of  solution) 

+  (Assay  of  tailings  X  Weight  of  pulp) 

For  quick  results,  the  bottles  are  placed  in  an  agitator 
which  is  revolved  for  twenty-four  hours. 

Several  agitation  tests  can  be  carried  out  in  this  manner, 
varying  the  quantity  of  cyanide  solution  used  and  the  mesh 
of  ore  (10-,  20-,  30-,  and  4O-mesh). 

Percolation. — For  these  tests  a  glass  percolating-jar  pro- 
vided with  a  false  bottom  covered  with  a  double  filter-paper 
will  be  found  convenient.  Such  an  apparatus  is  shown  in 
Fig.  I.  Place  I  pound,  or  more,  of  the  pulp  (with  the  proper 


APPENDIX  D. 


407 


quantity  of  the  neutralizer  thoroughly  mixed  with  it)  on  the 
filter,  and  add  to  the  charge  230  cc.  of  the  stock  solution  for 
each  pound  of  ore  taken.  Allow  the  solution  to  macerate 
for  twelve  hours,  and  then  percolate  gently  for  thirty  to  torty 
hours.  Wash  with  water  until  the  filtrate  reaches  the  original 
bulk.  The  rate  of  percolation  may  be  noted  here. 


ORE-> 
FILTER 


Apparatus  for  Test  by  Percolation. 

Test  the  solution  for  loss  of  cyanide;  assay  an  aliquot 
portion  of  the  solution  and  the  tailings,  and  thus  determine 
the  percentage  of  extraction. 

A  series  of  tests  may  be  carried  out  in  this  manner,  vary- 
ing the  strength  of  the  cyanide  solution,  the  fineness  of  the 
ore,  and  the  time  of  contact  from  twelve  to  seventy-two  hours. 

The  results  of  these  experiments  will  prove  the  applica- 
bility of  the  process  to  the  ore  in  question,  and  the  best 
method  of  treatment,  i.e.,  the  strength  of  solution  and  the 
mesh  which  will  give  the  best  extraction  in  the  shortest  time, 
with  the  least  consumption  of  cyanide. 

Where  it  is  desired  to  treat  larger  quantities  of  ore,  a  very 
convenient  apparatus  is  a  large  glazed  earthenware  jar,  pro- 
vided with  a  false  bottom  and  an  outlet  at  one  of  the  lower  sides. 


408  APPENDIX  D. 

The  following  formula  will  be  found  convenient  for  calcu- 
lating the  percentage  of  extraction: 

Let  A  =  the  assay-value  of    the  ore  in   ounces  troy  per 

ton  of  2000  pounds  av. ; 

B  =  milligrammes  of  gold  found  in  the  filtrate; 
C  =  pounds  av.  of  ore  taken  for  treatment ; 
X  =  the  percentage  of  extraction. 

ry 

X  —  6.43016^,. 

4.  Determination  of  the  Cause  of  Cyanide  Consumption. 

— Should  the  consumption  of  cyanide  be  high,  the  cause  of 
consumption  may  be  determined  by  an  analysis  of  the  cyanide 
solution.  For  every  part  of  cyanide  rendered  inoperative,  a 
corresponding  proportion  of  metal  enters  solution.  Thus  one 
part  by  weight  of  iron  consumes  seven  parts  by  weight  of 
potassium  cyanide,  etc.  The  following  equations  represent 
the  reactions  most  frequently  encountered: 

FeSO4  +  6KCN  =  K4Fe(CN)6  +  K2SO4 
or 

56  (at.  weight  of  Fe)  :  390  (mol.  wt.  6KCN)  : :  I  :  7. 

ZnSO4  +  4KCN  =  K2Zn(CN)4  +  K2SO4; 
or 

65  (at.  wt.  Zn)  :  260  (mol.  wt.  4KCN)  1:1:4. 
2  Cu"SO4  +  6KCN  =  K2Cu'2(CN)4  +  2K2SO4  +  2CN. 

Salts  of  aluminium  and  magnesium  act  in  a  different 
manner  with  potassium  cyanide,  their  hydrates  being  formed 
with  the  liberation  of  hydrocyanic  acid,  thus: 

A12(S04)3  +  6KCN  +  6H20  =  A12(OH)6  +  3K2SO4  +  6HCN 
MgS04  +  2KCN  +  2H20  =  Mg(OH)2  +  K2SO4  +  2HCN. 

A  preliminary  alkaline  treatment  overcomes  this  objection- 
able feature,  their  hydrates  being  precipitated,  which  are 
then  inert  towards  potassium  cyanide,  thus: 

MgS04  +  Ca(OH),  =  Mg(OH),  +  CaSO4, 


APPENDIX  D.  409 

insoluble  magnesium  hydrate  and  insoluble  calcium  sulphate 
being  formed. 

Soluble  sulphides,  formed  by  the  action  of  potassium 
cyanide  on  some  metallic  sulphides,  again  react  to  some 
extent  on  the  cyanide,  with  the  formation  of  sulpho-cyanide 
of  potassium,  thus: 

ZnS  +  4KCN  =  K2Zn(CN)4  +  K2S 
K2S  +  KCN  +  H20  +  O  =  2KOH  +  KCNS. 

To  determine  the  cause  of  the  consumption  of  cyanide 
place  100  grammes  of  the  pulp  in  a  wide-mouthed  bottle,  add 
200  cc.  of  the  cyanide  solution,  and  agitate  for  fifteen  hours. 
Filter,  take  20  cc.  of  the  filtrate  (equivalent  to  10  grammes 
of  ore)  and  evaporate  almost  to  dryness  in  a  porcelain  dish. 
Add  some  strong  sulphuric  acid,  evaporate  almost  to  dryness, 
and  cool.  Dilute  with  water,  add  some  hydrochloric  acid, 
and  heat  to  effect  solution  if  necessary.  The  metal  in  solu- 
tion may  now  be  determined  by  the  usual  methods. 

The  strong  sulphuric  acid  at  a  high  temperature  decom- 
poses the  metallic  cyanides,  thus: 


Ag2SO4  +  2NH4HSO4  +  2CO3  +  4H. 

Strong  nitric  acid  may  be  used  in  place  of  strong  sul- 
phuric; but  hydrochloric  cannot  be  used,  as  it  leaves  the 
metal  in  the  form  of  a  double  cyanide  salt,  which  is  soluble. 

The  reactions  with  nitric  and  hydrochloric  acids  are: 

AgCN  +  HNO3  +  2H2O  =  AgNO3  +  CO2  +  NH3  +  2H. 

K4Fe(CN)G  +  4HC1  =  H4Fe(CN)6  +  4KC1. 

5.  Determination  of  the    Cause  of  Non-Extraction.  — 

Should  the  above  tests  show  a  low  percentage  of  extraction, 
the  next  step  is  to  determine  the  cause  of  this  non-extrac- 
tion. It  may  be  due  to  numerous  causes,  such  as  total 
destruction  of  potassium  cyanide  by  certain  salts  of  the  base 
metals  present  in  a  form  readily  attacked  by  the  potassium 


4IO  APPENDIX  D. 

cyanide.  The  gold  may  be  in  a  very  coarse  state,  in  which 
case  the  solvent  action  of  the  potassium  cyanide  will  be  too 
slow  for  the  practical  application  of  the  process.  The  gold 
may  be  combined  or  alloyed  with  tellurium,  antimony,  bis- 
muth, etc.,  in  which  case  the  cyanide  is  inoperative  until  the 
combination  is  broken  up.  The  presence  of  soluble  sulphides 
in  solution.  The  character  of  the  gangue,  such  as  kaolin  or 
talc,  which  may  be  present  in  such  quantities  as  to  effectually 
prevent  percolation.  To  overcome  these  difficulties  the 
following  methods  may  be  tried : 

In  the  case  of  an  ore  which  consumes  a  large  quantity  of 
cyanide,  if  a  preliminary  wash  with  water,  weak  acid,  or  alkali 
is  ineffective,  the  ore  may  be  classed  as  one  not  adapted  to 
the  process. 

The  coarse-gold  difficulty  may  be  overcome  by  amalgama- 
tion, either  before  or  after  treatment  with  cyanide,  which 
generally  results  in  an  excellent  extraction.  The  South 
African  practice  may  be  cited  as  an  example. 

The  difficulty  due  to  the  presence  of  bismuth,  antimony, 
etc.,  in  combination  or  as  an  alloy  with  the  gold,  may  some- 
times be  overcome  by  fine  grinding  and  long  contact  with  the 
cyanide  solution;  but  the  usual  method  is  to  treat  the  ore  to 
a  preliminary  roast,  which  converts  the  gold  into  a  condition 
in  which  it  is  readily  attacked  by  cyanide. 

The  difficulty  due  to  the  presence  of  soluble  sulphides  can 
be  overcome  by  the  addition  of  a  soluble  lead  salt  or  the 
addition  of  an  oxidizing  agent. 

Should  the  ore  contain  much  kaolin  or  talc,  if  coarse 
crushing  is  ineffectual,  nothing  further  can  be  done,  and  the 
ore  must  be  classed  as  one  non-adapted  to  the  process. 

Ores  containing  considerable  quantities  of  oxidized  copper 
minerals  are  to  be  classed  as  not  adapted  to  the  process. 

6.  Determination  of  the  Free  Potassium  Cyanide  in 
Solution. — A  number  of  methods  have  been  proposed,  and 
there  are  several  which  give  good  results  when  the  solution  is 
free  from  cyanides  other  than  potassium  cyanide.  With  com- 
plex mill  solutions  containing  K2Zn(CN)4  these  methods  fail. 


APPENDIX  D.  411 

With  pure  solutions,  such  as  the  freshly  prepared  stock 
solution,  a  rapid  and  accurate  determination  may  be  made  by 
titrating  a  measured  quantity  of  the  solution  to  be  tested  with 
a  standard  solution  of  silver  nitrate,  using  2  or  3  drops  of  a  5 
per  cent  solution  of  potassium  iodide  as  an  indicator.  Silver 
cyanide  is  formed,  and  immediately  redissolves  in  the  excess 
of  potassium  cyanide.  The  reaction  is  as  follows: 

AgNO3  +  KCN  =  AgCN  +  KNO3; 

AgCN  +  KCN  =  KAg(CN)2 ; 

or  the  reaction  may  be  expressed  as  follows : 

2KCN  +  AgN03  =  KAg(CN)2  +  KNO3. 

As  soon  as  all  the  potassium  cyanide  has  been  converted 
into  the  double  cyanide  of  potassium  and  silver  an  additional 
drop  of  the  silver-nitrate  solution  produces  a  pale-yellow 
opalescence,  owing  to  the  formation  of  silver  iodide.  The 
quantity  of  silver  solution  added  is  read  off  from  the  burette 
and  the  percentage  of  potassium  cyanide  is  calculated. 

In  the  United  States  a  solution  containing  6.535  grammes 
of  silver  nitrate  to  the  liter  is  used.  The  quantity  of  cyanide 
solution  usually  taken  is  10  cc.  When  10  cc.  of  cyanide 
solution  are  taken,  each  cc.  of  the  silver  solution  used  indi- 
cates i  pound  of  potassium  cyanide  to  the  ton  (2000  pounds) 
of  solution.  Abroad,  decinormal  silver-nitrate  solution  is 
generally  employed,  the  loss  in  cyanide  being  obtained  in 
percentage  on  the  ore.  This  percentage  multiplied  by  20 
gives  the  pounds  of  potassium  cyanide  consumed  per  ton. 

Another  method  which  answers  all  purposes,  provided  the 
cyanide  solutions  are  quite  pure,  but  which  is  useless  for 
complex  mill  solutions,  depends  upon  the  following  reaction: 

KCN  +  2l  =  KI  +  ICN. 

This  method  requires  a  solution  of  pure  iodine  in  potas- 
sium iodide.  A  solution  of  pure  wheat  starch  is  used  as  an 
indicator.  Ten  or  more  cc.  of  the  cyanide  solution  are  meas- 


APPENDIX  D. 

ured  off  and  run  into  a  beaker.  A  few  drops  of  the  starch 
solution  are  added,  and  then  the  iodine  solution  is  run  in  from 
a  burette,  with  stirring,  until  an  excess  of  one  drop  of  the 
iodine  solution  is  present,  which  is  indicated  by  the  formation 
of  permanent  blue  iodide  of  starch.  The  iodine  solution  may 
be  standardized  by  some  freshly  prepared  stock  solution,  or 
preferably  by  means  of  a  standard  solution  of  sodium  hypo- 
sulphite. This  method  may  be  used  to  determine  the  per- 
centage of  KCN  in  commercial  potassium  cyanide. 

A  number  of  other  methods  for  the  determination  of  the 
available  cyanide  have  been  proposed,  but  that  first  described 
is  believed  to  be  the  best. 

In  a  well-regulated  mill  the  strength  of  the  solutions  is 
tested  on  each  tank  every  four  hours  whilst  the  solutions  are 
percolating, 

The  method  usually  adopted  for  the  determination  of  the 
free  potassium  cyanide  in  mill  solutions  is  as  follows:  10  cc. 
of  solution  are  diluted  with  distilled  water  to  65  or  70  cc.  and 
titrated  with  the  standard  silver-nitrate  solution,  without  the 
use  of  an  indicator.  When  all  the  free  potassium  cyanide  is 
changed  to  KAg(CN)a  an  additional  drop  of  the  silver  solution 
produces  a  distinct  white  opalescence,  owing  to  the  formation 
of  insoluble  zinc  cyanide,  thus: 

K2Zn(CN)4  +  AgN03  =  KAg(CN)2  +  Zn(CN)2  +  KNO3. 

It  is  probable  that  this  second  reaction  commences  before 
all  the  potassium  cyanide  is  combined  with  silver;  for  on 
partly  titrating  a  solution  containing  both  salts,  and  allowing 
it  to  stand,  a  white  precipitate  slowly  forms.  Hence  the 
titration  must  be  performed  rapidly,  in  which  case  the  separa- 
tion of  the  white  precipitate  can  be  taken  as  marking  the  end- 
point.  The  titration  requires  some  practice  to  be  performed 
properly. 

7.  Determination  of  the  Free  Hydrocyanic  Acid  in 
Solution. — To  10  cc.  of  the  mill  solution  add  10  cc.  of  a 
solution  of  potassium  bicarbonate  (containing  15  grammes  of 
KHCO,  to  the  litre),  dilute  to  65  or  70  cc.  and  titrate  as  in 


APPENDIX  D.  41  I  £ 

f  e-st  6,  without  the  use  of  potassium  iodide  as  an  indicator. 
Upon  the  addition  of  the  bicarbonate  the  following  reaction 
takes  place: 

HCN  +  HKCO,  =  KCN  +  CO,  +  H3O. 

The  titration  gives  the  HCN  in  terms  of  KCN,  and  KCN 
X  0.415  —  HCN.  As  this  titration  gives  the  potassium 
cyanide  and  the  hydrocyanic  acid,  the  difference  between  this 
result  and  that  obtained  in  Test  6,  multiplied  by  0.415,  gives 
the  hydrocyanic  acid. 

For  each  cc.  of  mill  solution  taken  I  cc.  of  the  potassium 
bicarbonate  solution  is  used.  This  will  be  sufficient  for  solu- 
tions containing  as  much  as  0.4  per  cent  of  HCN,  which  is 
much  higher  than  mill  solutions  usually  run,  but  the  excess 
does  no  harm. 

The  addition  of  the  bicarbonate  solution  usually  causes  a 
distinct  turbidity,  which  should  disappear  when  the  solution 
is  diluted,  giving  a  clear  liquid  for  titration.  If,  as  rarely 
happens,  a  faint  turbidity  remains,  a  duplicate  of  the  solution 
to  be  titrated  is  prepared,  the  end-point  being  shown  by  the 
increased  cloudiness  in  the  titrated  solution  as  compared  with 
the  blank  solution. 

8.  Determination  of  the  Total  Simple  Cyanides  in 
Solution. — To  10  cc.  of  the  mill  solution  add  10  cc.  of  half- 
normal  sodium-hydrate  solution  (20  grammes  of  NaOH  per 
litre),  dilute  to  65  or  70  cc.,  add  a  few  drops  of  the  potassium- 
iodide  solution,  and  titrate  to  pale-yellow  opalescence,  as  in 
Test  6.  The  result  is  the  total  KCN,  HCN,  and  K2Zn(CN)4, 
in  terms  of  KCN.  The  amount  of  sodium  hydrate  to  be 
added  depends  principally  on  the  percentage  of  K2Zn(CN)4 
present,  as  a  large  excess  should  be  avoided.  The  amount 
given  will  be  sufficient  for  solution's  containing  0.7  per  cent 
zinc  and  0.4  per  cent  hydrocyanic  acid,  and  will  answer  in  all 
ordinary  cases  likely  to  be  encountered  in  mill  practice.  The 
addition  of  the  sodium  hydrate  produces  a  permanent  precipi- 
tate, but  the  use  of  potassium  iodide  as  an  indicator  prevents 
any  doubt  as  to  the  end-reaction. 


41 1C  APPENDIX  D. 

9.  Determination  of  the   Ferro-,   the   Ferri-,  and  the 
Sulpho-Cyanides  in   Solution. — The  ferrocyanides  and  the 
sulphocyanides,   if  desired,    may  be  determined  by  titration 
with  a  standard  solution  of  potassium  permanganate  in  an 
acid  solution,  trie  reactions  being  as  follows: 

ioK4FeCy6+  K2Mn2O8  +  8H2SO4  =  ioK3FeCye+ 6K2SO4  + 
2MnSO4+8H2O; 

loKCyS  +  6K9Mn2O8  +  isH2SO4  =  i  iK2SO4  +  i2MnSO4  + 
ioHCy+8H2O. 

One  portion,  acidified  with  sulphuric  acid,  is  titrated,  the 
result  representing  both  of  the  above  compound  cyanides. 
To  a  second  portion,  acidified  with  sulphuric  acid,  a  solution 
of  ferric  chloride  is  added.  The  resulting  Prussian  blue  is 
filtered  off  and  the  filtrate  is  titrated  with  the  standard  per- 
manganate solution.  This  second  titration  gives  the  potas- 
sium sulphocyanide. 

The  permanganate  solution  should  be  quite  dilute,  con- 
taining not  more  than  from  0.3  to  0.5  gramme  of  potassium 
permanganate  to  the  litre.  It  may  be  standardized  by  any 
of  the  approved  methods,  and  its  value  may  be  calculated 
for  the  compound  cyanides  according  to  the  above  equations. 

Ferricyanide,  if  present,  may  be  determined  by  reducing 
it  to  ferrocyanide,  and  then  by  titration  with  standard  potas- 
sium permanganate  as  above. 

Should  sulphides  be  present,  the  shaking  up  of  the  solu- 
tion with  moist  lead  carbonate  will  produce  a  black  precipitate 
of  lead  sulphide.  When  present,  they  must  be  thus  removed, 
by  agitation  with  lead  carbonate  and  filtering  off  the  resulting 
lead  sulphide,  before  the  compound  cyanides  can  be  deter- 
mined. 

10.  Determination  of  the  Zinc  and  Lime  in  Solution. 
— As  these  are  sometimes  of  considerable  importance,  they 
have  to  be  occasionally  determined  in  the  mill  solutions.     The 
solution   is  treated   in  the   manner  described   in   Test  4,  and 
the  lime  and  zinc  can  then  be  determined  by  conventional 
methods. 


APPENDIX  D.  <\l\d 

II.  Determination  of  the  Gold  and  Silver  in  Solution. 
' — Numerous  methods  have  been  proposed,  but  the  following, 
which  is  the  simplest,  is  the  method  generally  adopted : 

Evaporate  one  assay-ton  (—  29.2  cc.)  of  the  solution  to 
dryness  in  a  lead  tray.  Roll  up  the  lead  and  cupel  on  a  hot 
cupel,  weighing  the  resulting  button.  Alloy  the  bead  with 
silver,  if  necessary,  and  part  for  gold  as  usual. 

Should  the  solution  contain  over  0.2  ounce  of  gold  per 
ton,  the  lead  should  be  scorified  together  with  a  little  borax 
glass  prior  to  cupellation. 

The  lead  tray  is  made  of  pure  lead-foil,  and  is  3  inches 
long,  2  inches  wide,  and  -J  inch  deep.  It  should  weigh  about 
20  grammes.  For  the  evaporation,  the  tray  containing  the 
solution  is  placed  on  a  piece  of  asbestos  cardboard,  heated 
by  a  burner  underneath. 


APPENDIX  E. 


THE  ANALYSIS  OF  REFINED  COPPER. 

THE  following  method  of  sampling  a  lot  of  copper  is  quite 
generally  adopted :  Each  bar  or  ingot  is  drilled,  the  drillings 
being  taken  clear  through  the  bar.  These  drillings  are  melted 
in  a  clean  plumbago  crucible,  the  melt  being  cast  into  a  bar  or 
granulated  by  pouring  into  water.*  The  bar,  is  drilled  in 
several  places,  these  drillings  constituting  the  sample.  In  the 
case  of  a  granulated  sample  the  granulations  are  reduced  by 
quartering  for  the  final  assay  sample. 

Electrolytic  copper  may  contain  any  or  all  of  the  following 
impurities  :  Silver,  lead,  arsenic,  antimony,  selenium,  tellurium, 
bismuth,  iron,  sulphur,  and  oxygen. 

Silver. — For  the  determination  of  the  silver  weigh  out  30  to 
100  grammes,  dissolve  in  nitric  acid,  and  proceed  according  to 
Chapter  IV  of  Part  III,  except  that  it  is  unnecessary  to  make 
two  filtrations  where  gold  is  absent,  as  is  generally  the  case. 

Lead  and  Iron. — Introduce  from  10  to  30  grammes  into  a 
No.  4  beaker  and  dissolve  in  nitric  acid  (i  part  strong  acid  and 
I  part  water),  taking  care  to  use  no  more  acid  than  is  neces- 
sary. When  solution  is  effected,  heat  to  expel  the  red  fumes 
and  the  excess  of  acid,  dilute  to  300  cc.  with  water,  add  i  cc. 
of  sulphuric  acid,  stir,  and  allow  to  stand  for  several  hours. 
Filter  off  the  precipitated  lead  sulphate  and  wash  with  a  one 
per  cent  solution  of  sulphuric  acid  until  the  washings  are  free 
from  copper  salts.  The  lead  may  now  be  determined  ac- 
cording to  Chapter  IX  of  Part  II,  preferably  by  Alexander's 
method. 

*  The  melting  of  the  borings  is  condemned  by  Ulke.  The  Mineral  Indus- 
try, Vol.  III. 

412 


APPENDIX  E.  413 

To  the  filtrate  add  an  excess  of  ammonia  and  heat  to  boil- 
ing. The  iron  is  precipitated  together  with  arsenic,  etc. 
Filter  off  the  precipitate,  wash  it  with  hot  water  until  free 
from  copper  salts,  and  dissolve  it  on  the  filter  with  a  little  hot 
dilute  hydrochloric  acid.  Dilute  the  solution,  pass  sulphuret- 
ted hydrogen  for  30  minutes,  filter  off  the  precipitated  sulphides, 
wash  with  sulphuretted  hydrogen  water,  and  determine  the 
iron  in  the  filtrate  with  a  standard  solution  of  potassium  per- 
manganate according  to  Chapter  XVI  of  Part  II. 

Arsenic. — Dissolve  10  to  20  grammes  in  nitric  acid,  heat  to 
expel  red  fumes,  add  a  small  crystal  (about  I  gramme)  of  ferric 
sulphate,  stir,  and  add  an  excess  of  ammonia.  Heat  to  boil- 
ing, and  filter  off  the  precipitated  ferric  hydrate,  which  will 
contain  all  of  the  arsenic.  Wash  with  dilute  ammonia  water, 
dry,  and  ignite  the  precipitate.  Weigh  the  ignited  precipitate, 
reduce  it  to  an  impalpable  powder  in  an  agate  mortar,  weigh 
out  an  aliquot  portion,  and  fuse  it  with  8  parts  of  a  mixture  of 
pure  sodium  carbonate  and  potassium  nitrate.  Dissolve  the 
fused  mass  in  water,  and  determine  the  arsenic  according  to 
Chapter  X  of  Part  II. 

Antimony  and  Bismuth. — Dissolve  from  10  to  30  grammes 
in  nitric  acid,  heat  to  expel  red  fumes,  dilute  to  about  300  cc., 
and  add  a  small  crystal  of  pure  ferric  sulphate.  Render  the 
solution  ammoniacal,  heat  to  boiling,  add  0.75  gramme  of  am- 
monium carbonate  and  a  little  sodium  phosphate.  The  pre- 
cipitation of  bismuth  and  antimony  is  complete.  Filter  off  the 
precipitate,  wash  with  water  containing  a  little  ammonia,  and 
dissolve  the  precipitate  in  a  little  dilute  hydrochloric  acid. 
Dilute  the  solution  and  pass  sulphuretted  hydrogen  for  30  min- 
utes. Add  10  cc.  of  yellow  ammonium  sulphide  and  warm 
gently  for  one  hour.  Filter  and  wash.  The  filtrate  will  con- 
tain the  antimony,  which  is  precipitated  by  the  addition  of  a 
little  dilute  hydrochloric  acid.  Filter,  wash,  and  dissolve  the 
antimony  sulphide  with  a  little  warm  concentrated  hydro- 
chloric acid,  leaving  the  arsenic  sulphide  undissolved.  Dilute 
the  filtrate,  pass  sulphuretted  hydrogen,  allow  the  precipitated 
antimony  sulphide  to  settle,  wash  by  decantation,  and  finally 


4H  APPENDIX  E. 

transfer  to  a  weighed  porcelain  crucible.  Ignite  and  weigh  as 
Sb2O4 .  (See  Chapter  XI  of  Part  II.) 

The  residue  will  contain  the  bismuth,  with  probably  some 
lead  and  copper.  It  is  dissolved  in  nitric  acid  and  the  bis- 
muth is  precipitated  with  ammonium  carbonate  and  ammonia. 
The  precipitate  is  filtered  off  and  washed  with  water  contain- 
ing a  little  ammonia.  Should  the  copper  not  be  completely 
separated,  redissolve  in  a  little  nitric  acid  and  repeat  the  pre- 
cipitation. Dissolve  the  precipitate  on  the  filter  in  a  little 
nitric  acid  and  determine  the  bismuth  electrolytically  in  a 
dilute-  solution,  or  according  to  Chapter  XIV  of  Part  II. 
Should  the  bismuth  be  determined  electrolytically,  any  lead 
present  will  not  interfere,  as  it  will  be  separated  by  the  elec- 
trolysis (see  Table  VI).  This  method  is  due  to  Ray.* 

Tellurium  and  Selenium. — Dissolve  from  25  to  50  grammes 
of  the  copper  in  nitric  acid,  adopting  the  same  precautions  as 
in  the  case  of  lead  and  arsenic.  Add  to  the  solution  one 
gramme  of  ferric  nitrate,  stir,  and  heat  the  solution  to  boiling. 
Precipitate  the  iron  with  an  excess  of  ammonia,  when  the  pre- 
cipitate will  contain  all  the  tellurium  and  selenium.  The  pre- 
cipitated ferric  hydrate  is  filtered  off,  washed  with  water  con- 
taining a  little  ammonia,  and  dissolved  in  a  little  warm  dilute 
hydrochloric  acid.  To  the  solution  add  one  gramme  of  tar- 
taric  acid,  render  alkaline  with  an  excess  of  potassic  hydrate, 
and  pass  sulphuretted  hydrogen  for  30  minutes.  Filter  and 
precipitate  the  tellurium  and  selenium  in  the  filtrate  by  the 
addition  of  hydrochloric  acid.  Warm  to  expel  the  sulphuret- 
ted hydrogen,  and  when  it  is  all  expelled  filter  off  the  sulphides 
of  tellurium  and  selenium.  Dissolve  the  washed  precipitate  in 
aqua  regia,  evaporate  the  solution  to  dryness  to  expel  the 
nitric  acid,  repeating  the  evaporation  if  necessary,  and  dissolve 
the  dry  mass  in  hydrochloric  acid.  Pass  sulphurous  acid  gas 
through  the  solution,  and  filter  off  the  precipitated  tellurium 
and  selenium  into  a  weighed  filter.  Wash  the  precipitate  with 
warm  water,  allow  to  stand  in  a  warm  place  for  12  hours,  and 


*The  Mineral  Industry,  Vols.  I,  II,  and  III. 


APPENDIX  E.  415 

weigh.  To  separate  the  tellurium  and  selenium  place,  the  pre- 
cipitate in  a  small  casserole,  add  an  excess  of  a  strong  solution 
of  potassium  cyanide,  and  boil.  When  solution  is  effected,  add 
hydrochloric  acid,  which  will  precipitate  the  selenium,  leaving 
the  tellurium  in  solution.  Filter,  wash,  dry  at  100°  C,  and 
weigh  the  selenium.  This  method  is  due  to  Whitehead.* 

Sulphur. — Place  10  to  20  grammes  of  the  copper  in  a  No. 
4  beaker  and  add  60  cc.  of  nitric  acid  (1.42  sp.  gr.)  and  15  cc. 
of  hydrochloric  acid  (1.20  sp.  gr.).  Heat  over  an  alcohol 
flame,  and  when  solution  is  effected  raise  the  lamp-wick  and 
evaporate  nearly  to  dryness.  Add  50  cc.  of  strong  nitric  acid 
and  repeat  the  evaporation.  Repeat  the  operation,  redissolve 
in  300  cc.  of  water,  and  add  a  little  nitric  acid  if  a  trace  of 
basic  salt  remains  undissolved.  The  addition  of  hydrochloric 
acid  and  the  subsequent  evaporation  with  nitric  acid  may 
be  dispensed  with,  provided  experiment  shows  that  nitric 
acid  alone  will  oxidize  all  the  sulphur  in  the  material  operated 
upon.  Pour  the  solution  through  a  small  filter  into  a  700  cc. 
beaker  and  dilute  with  distilled  water  to  600  cc.  Introduce  a 
sheet  of  platinum  (4  by  5  inches)  into  the  solution  as  a  nega- 
tive electrode,  and  as  a  positive  electrode  a  small  coil  of  plat- 
inum wire.  Cover  the  beaker  with  a  wratch-glass  and  connect 
the  electrodes  with  the  battery  or  an  incandescent  lamp  circuit. 
Two  i6-candle-power  lamps,  coupled  in  parallel,  will  deposit 
the  copper  in  one  night.  When  the  copper  is  all  deposited, 
remove  the  electrodes,  wash  them  with  distilled  water,  allow- 
ing the  washings  to  run  into  the  solution,  and  filter.  Add  to 
the  filtrate  o.i  gramme  (for  crude  copper  0.5  gramme)  of  pure 
dry  sodium  carbonate,  and  evaporate  the  solution  to  dryness  in 
a  No.  3  or  No.  4  porcelain  casserole.  An  alcohol  lamp  should 
be  used,  and  the  solution  should  be  protected  from  dust,  etc. 
When  the  salts  in  the  dish  are  dry,  heat  the  covered  casserole 
quite  strongly,  with  the  lamp  held  in  the  hand,  until  the  acid 
ammonium  nitrate  suddenly  volatilizes,  and  then  allow  it  to 
cool. 

*  Journal  of  the  Am.  Chem.  Society,  Vol.  XVII,  p.  280. 


APPENDIX  E. 

At  this  point  is  the  only  danger  of  loss  of  sulphur,  hence 
the  heat  should  be  just  high  enough  to  volatilize  the  nitrate. 

Add  to  the  residue  10  cc.  of  strong  hydrochloric  acid  and  5 
cc.  of  water,  and  evaporate  to  dryness  on  the  water-bath.  Re- 
peat this  operation  and  then  add  I  cc.  of  strong  hydrochloric 
acid  and  50  cc.  of  water  ;  heat  to  effect  solution,  filter  into  a 
small  beaker,  and  wash  with  hot  water. 

The  only  impurity  which  is  liable  to  be  present  which  will 
interfere  with  this  method  is  lead.  Should  any  lead  sulphate 
remain  on  the  filters,  they  must  be  boiled  with  a  solution  of  pure 
sodium  carbonate,  and  after  filtration  the  solution  is  acidified 
with  hydrochloric  acid,  and  the  sulphur  removed  by  precipita- 
tion with  barium  chloride.  The  weight  of  barium  sulphate 
thus  recovered  should  be  added  to  the  weight  of  the  main 
precipitate. 

Heat  the  solution  of  sodium  sulphate  to  boiling,  precipitate 
with  a  slight  excess  of  barium  chloride,  and  allow  the  precipi- 
tate to  settle  24  hours.  When  rapid  results  are  desired,  the 
solution  may  be  kept  at  a  temperature  of  75°  C.  for  three 
hours  and  then  filtered.  The  sulphur  is  now  determined  in 
the  usual  manner.  This  method  is  due  to  Heath.* 

Oxygen. — For  the  determination  of  the  oxygen  a  special 
sample  should  be  prepared  by  filing  the  bar  with  a  small  velvet 
file.  The  filings  are  freed  from  dirt  with  a  pincers,  and  from 
iron  with  the  magnet.  Samples  of  5  grammes  each  are  intro- 
duced into  porcelain  boats,  and  the  boat  is  placed  in  a  glass 
or  platinum  ignition  tube.  The  samples  in  the  tube  are  now 
ignited  in  a  stream  of  pure  hydrogen  gas  in  the  usual  manner. 
The  loss  in  weight  of  each  sample  upon  ignition  represents 
oxygen. 

*  Journal  of  the  Am.  Chem.  Society,  Vol.  XVII,  p.  814. 


APPENDIX   F 


THE  MECHANICAL  ASSAY  OF  GOLD  AND  SILVER 

ORES. 

THE  assayer  is  sometimes  called  upon  to  test  gold  and  silver 
ores  to  determine  the  percentages  of  the  precious  metals  which 
can  be  extracted  and  saved  by  amalgamation  processes.  He 
may  also  be  required  to  test  ores  of  gold,  silver,  copper,  lead, 
etc.,  to  determine  whether  the  ores  can  be  successfully  con- 
centrated. Some  gold  and  silver  ores  are  most  successfully 
treated  by  a  combination  of  the  amalgamation  and  concentra- 
tion processes ;  in  fact,  a  great  majority  of  the  gold  and  silver 
ores  of  Western  America  and  elsewhere  can  be  treated  by 
these  methods,  in  which  case  combination  tests  are  in  order. 
The  average  mining  man  seems  to  have  the  idea  that  the 
process  to  be  adopted  can  only  be  determined  after  many  tons 
of  the  ore  have  been  shipped  to  some  working  mill  and  there 
treated.  This  method  of  testing  an  ore  by  a  mill-run  presents 
certain  advantages  and  is  to  be  recommended,  where  it  can 
be  economically  and  successfully  carried  out,  but  it  necessitates 
the  mining  and  shipment  of  a  considerable  quantity  of  ore, 
as  it  is  impossible  to  make  a  reliable  quantitative  test  in  this 
manner  on  a  few  tons  of  material  on  account  of  the  difficulty 
of  making  an  accurate  "  clean-up."  It  involves  the  careful 
supervision  of  an  expert  at  the  mill  during  the  test,  while  the 

417 


41 8  APPENDIX  F. 

nearest  available  mill  may  be  far  distant,  in  which  case  the 
expense  involved  will  be  considerable.  The  nearest  available 
mill  may  be  totally  unsuited  to  the  proper  treatment  of  the 
ore  in  question,  and  a  mill  which  is  adapted  to  the  treatment 
of  the  ore  may  not  be  obtainable  within  hundreds  or  thousands- 
of  miles.  By  this  method  a  great  deal  of  time  and  money 
may  be  wasted  in  making  an  unnecessary  test ;  on  the  other 
hand,  the  results  obtained  are  actual  working  results,  obtained 
in  a  working  mill,  and  hence  appeal  to  the  uninitiated.  It  is 
the  opinion  of  the  author,  after  many  years  of  practical  ex- 
perience in  testing  ores  both  in  the  mill  and  the  laboratory, 
that  the  laboratory  method  is  preferable  in  most  cases.  It  can 
be  carried  out  on  the  ground ;  it  involves  less  expense ;  it  does 
not  involve'  the  actual  mining  of  tons  of  ore  with  which  to 
make  the  test ;  the  results  may  be  obtained  quickly,  and  the 
conditions  essential  to  the  successful  treatment  of  the  ore 
may,  in  most  cases,  be  determined  more  accurately  in  the 
laboratory  than  they  can  be  in  the  mill. 

No  matter  how  much  engineers  may  disagree  with  the  above 
statements,  they  might  all  well  agree  that  preliminary  labora- 
tory tests  should  always  precede  the  actual  mill  tests,  in  the 
examination  of  a  mining  property.  Many  mining  districts 
contain  the  ruins  of  reduction-works  which  were  erected  to 
treat  ores  which  were  either  wanting  in  quantity  or  were 
totally  unsuited  to  the  method  of  treatment  adopted.  How 
much  wasted  money  could  have  been  saved  by  a  little  prelim- 
inary testing  ?  Want  of  intelligence,  or  care,  in  the  sampling 
and  estimation  of  ore  bodies,  and  a  disregard  of  metallurgical 
principles  and  economic  conditions,  are  responsible  for  a 
majority  of  such  failures. 

CONCENTRATING  TESTS. 

The  method  to  be  pursued  will  depend  largely  upon  the 
appliances  at  hand  and  whether  this  is  to  be  a  preliminary  or 
a  final  test.  It  may  happen  that  the  only  apparatus  obtainable 
are  the  hand-mortar,  bucking-plate,  gold-pan,  and  a  few  sieves, 


APPENDIX  F.  419 

in  which  case  the  tests  are  made  by  hand.  These  hand  tests 
can  hardly  be  taken  as  a  criterion  of  what  may  be  actually 
accomplished  in  a  properly  constructed  mill,  but  are,  never- 
theless, extremely  valuable  as  an  indication  of  what  may  be 
accomplished,  and  are  frequently  all  that  will  be  required. 

Hand  Tests. — The  first  step  in  all  tests  is  a  critical  eye 
inspection  of  the  ore  in  order  to  determine  its  mineral  char- 
acter and  approximately  the  percentages  of  its  various  mineral 
constituents.  Sometimes  this  is  as  far  as  the  investigation 
need  proceed,  as  the  inspection  may  show  the  ore  to  be  un- 
suited  to  concentration.  If  the  character  of  the  ore  and  the 
percentages  of  the  gold-carrying  minerals  appear  such  as  to 
lead  one  to  believe  the  ore  may  be  concentrated,  the  next  step 
is  to  determine  how  fine  the  ore  should  be  crushed.  •  This  may 
be  settled,  in  a  preliminary  way  at  least,  by  crushing  typical 
pieces  of  the  ore  and  examining  the  different  sized  particles 
with  the  aid  of  a  magnifying-glass.  It  must  be  remembered 
that  fine  crushing  is  nearly  always  a  disadvantage ;  but,  on  the 
other  hand,  it  is  necessary  to  crush  the  ore  sufficiently  to 
liberate  or  separate  the  valuable  minerals  from  the  gangue. 

Having  settled  the  point  as  to  how  fine  it  is  desirable  to 
crush  the  ore,  a  sample  of,  say,  five  pounds,  is  crushed  to  this 
size.  The  sample  should  be  crushed  in  successive  stages,  the 
fines  being  screened  out  as  the  crushing  progresses,  in  order  to 
avoid  an  undue  amount  of  slimes.  The  hand-mortar  and  a 
nest  of  box-sieves  will  serve  for  this  purpose.  The  sieve 
frame  and  box  of  the  nest  shown  in  Fig.  I  are  of  tin,  the 
sieves,  except  the  4-mesh,  are  of  brass  cloth,  and  the  pan- 
box  is  12  inches  in  diameter.  For  these  hand  tests  it  is  not 
desirable  to  make  a  number  of  different  sizes,  as  only  com- 
paratively fine  material  can  be  treated  in  the  panrconsequently 
the  ore  is  crushed  to  pass  a  certain  mesh  sieve  ;  generally  20 
or  30  mesh  will  prove  to  be  the  proper  size.  After  the  sample 
is  crushed  and  screened  it  is  dried  on  a  steam  drier,  the  dried 
pulp  is  spread  out  on  a  piece  of  rubber  cloth,  or  heavy  paper, 
and  a  sample  for  assay  (about  six  ounces)  is  carefully  taken. 


420 


APPENDIX  F. 


The  assay  sample  is  pulverized  on  the  bucking-plate  to  pass  a 
loo-mesh  sieve.  From  the  remainder  of  the  material  a  sample 
of,  say,  4  pounds,  is  weighed  out  and  concentrated  by  panning 
in  the  gold-pan  illustrated  in  Fig.  2.  The  tailings  from  this 
panning  operation  are  caught  in  a  large  tin  milk-pan,  or  other 
suitable  vessel,  and  allowed  to  settle.  The  concentrates  re- 
maining in  the  gold-pan  are  examined  from  time  to  time  to 
see  if  they  are  sufficiently  free  from  gangue, 
and  are  washed  off  into  a  small  tin  sample 
pan.  When  all  of  the  4-pound  sample  has 
been  treated  in  this  way  the  tailings  are 
settled  and  examined  with  the  magnifying- 
glass.  Should  they  be  found  to  contain  much 
valuable  mineral  they  are  repanned,  the  re- 
sulting concentrates  being  added  to  the  first 
batch.  This  operation  may  have  to  be  re- 
peated once  or  twice  in  order  to  obtain  clean 
tailings,  and  even  then  the  tailings  may  show 
considerable  valuable  mineral  in  the  finer 
FIG.  i.  sizes  or  adhering  to  the  larger  particles  of 

gangue.  In  this  case  the  tailings  are  dried  and  crushed  to 
pass  a  finer  screen,  say  50  or  60  mesh.  This  material  is  mixed 
with  water  in  a  large  tin  pan  and  is  carefully  washed  on  the 
vanning-plaque  or  vanning-shovel,  illustrated  in  Figs.  3  and  4. 
The  concentrates  from  this  operation  are  washed  into  a  small 
sample  pan  and  dried,  while  the  tailings  are  added  to  those 
resulting  from  the  panning.  Each  sample  of  dried  concen- 
trates is  weighed  and  a  small  assay  sample  is  carefully  cut  out 
of  each  lot.  The  assay  sample  is  ground  on  the  bucking-plates 
to  pass  a  loo-mesh  screen  and  assayed.  The  tailings  are  also 
dried  and  weighed,  and  an  assay  sample  is  cut  out.  The  tail- 
ings should  be  retained  for  further  tests  by  amalgamation,  or 
other  methods,  should  such  tests  be  considered  advisable  after 
the  various  samples  are  assayed. 

The  method  of  calculating  the  results  is  illustrated  in  the 
following  example  :  Ore,  iron  pyrites  ;  gangue,  quartz. 


APPENDIX  F. 


42I 


Weight. 
Ounces, 
Avoir. 

Assay.    Oz.  per 
Ton  of  2000  ibs. 

Percentage  of  Total. 

Gold. 

Silver. 

Mineral 

Gold. 

Silver. 

50.0 
6.5 

I.O 

40.6 
1.9 

7-5 

1.2 

7.0 

7-9 
0.  12 

6.0 
21.0 
46.0 
2.0 

13-0 

2.O 
81.2 

3.8 
15-0 

IOO.OO 

75.83 

13.16 

8.02 
3-09 
88.99 

100.  0 

45-5 
15.3 
13-5 
25-7 
60.8 

Concentrates  from  panning  

Saved  in  concentrates    •  • 

FIG  2. 


Such  tests  are,  of  course,  only  approximations  ;  and  while 
they  are  not  sufficiently  thorough  to  enable  one  to  plan  a  mill 
for  the  proper  treatment  of  an  ore,  they  are  extremely  useful 
in  out-of-way  places,  and  will  serve  as  a  guide  to  the  proper 
method  of  treatment  to  be  adopted.  Before  the  engineer  can 
make  a  report  as  to  just  how  an  ore  should  be  concentrated,  what 
machines  should  be  used,  how  the  machines  should  be  arranged 
and  adjusted,  what  the  probable  cost  of  treatment  will  be,  and 
many  other  details,  several  points  in  the  treat- 
ment of  the  ore  have  to  be  determined.* 
Assuming  that  the  preliminary  tests  were 
satisfactory,  as  in  the  case  of  the  above  ex- 
ample, to  determine  these  points  a  large  quan- 
tity of  the  ore  should  be  shipped  to  some  concentrating  mill 
and  treated,  or  the  following  machine  tests  should  be  made. 

Machine  Tests. — For  testing  small  quantities  of  ore  the 
writer  knows  of  no  apparatus  which  is  better  adapted  to  the 
work  than  the  Vezin  laboratory  jig  for  treating  the  coarser 
sizes,  followed  by  the  Richards  tube  for  classification  of  the 
finer  sizes,  which  are  then  treated  on  the  jig,  vanning-shovel, 
or  vanning-plaque. 

The  Vezin  jig,  illustrated  in  Fig.  5,  was  designed  by  Mr. 
Henry  A.  Vezin,  of  Denver,  Col.,  for  the  purpose  of  making 

*  The  reader  is  referred  to  the  author's  articles  on  "  Concentration  of 
Gold  Ores,"  published  in  Mines  and  Minerals  for  April,  May,  June,  July, 
and  August,  1897. 


OFTIOI        *K*. 

UNIVERSITY 


422 


APPENDIX  F, 


concentrating  tests  in  the  laboratory.  Mr.  Vezin  has  also  de- 
signed a  jig  with  a  bed  6  by  12  inches,  having  six  times  the 
capacity  of  the  smaller  one,  and  being  also  arranged  for  hand 
power,  though  it  was  found  best  to  use  a  2-inch  belt  and  power 
for  driving  it.  This  jig  is  useful  for  treating  samples  of  ore 
from  600  to  1000  pounds  in  weight  ;  but  the  small  jig  will 
generally  be  found  most  convenient.  The  jig  consists  of  a 
screen  compartment  A,  connected  with  the  hutch,  as  in  the 
ordinary  large  jig.  Into  the  compartment  A  is  fitted  the  screen- 
box  y/  In  the  illustration,  one  of  the  screen-boxes  is  shown  in 
place  in  the  machine  and  two  extra  boxes  are  shown  on  the 


FIG.  3. 


FIG.  4. 


table.  The  screen-box  in  place  is  provided  with  a  stay-box  P, 
and  is  used  when  fine  material  is  treated  or  where  it  is  desirable 
to  jig  under  water.  The  screens  and  plunger  are  3  by  4  inches, 
and  the  plunger  has  a  clearance  all  around  of  -£%  inch.  In  a 
later  machine  the  screen-boxes  are  dispensed  with,  the  screens 
being  held  in  place  by  brass  collars  attached  to  the  jig  com- 
partment and  held  together  ,by  means  of  clamps.  The  screen 
compartment,  hutch,  plunger  compartment,  and  screen-boxes 
are  of  No.  XXX  tin  or  No.  22  brass.  The  screens  are  of  woven 
brass  wire.  The  plunger  compartment,  shown  at  B,  is  pro- 
vided with  a  brass  piston  with  rubber  packing.  The  plunger 
rod  is  operated  by  an  eccentric  D,  arranged  so  that  the  stroke 
can  be  readily  varied  from  o  to  ij  inches.  -The  machine  may 
be  operated  by  hand  by  means  of  the  crank  G  and  the  gear- 


APPENDIX  F. 


423 


wheels  E  and  F,  geared  3  to  I,  so  that  without  moving  the 
hand  very  quickly  a  speed  of  from  200  to  240  revolutions  can 
be  attained.  The  machine  may  also  be  driven  by  power  by 
means  of  the  small  wooden  pulley  K  and  the  friction  gears  C 
and  L.  This  friction  gearing  is  thrown  in  or  out  by  the  spring 
N,  and  the  small  wheel  L  is  adjustable  on  the  shaft,  so  that 


FIG.  5. 

the  number  of  strokes  can  be  readily  varied.  The  large  disk  C 
has  three  rings,  marked  respectively  100,  200,  and  300.  These 
represent  the  revolutions  per  minute  which  the  eccentric  will 
make  when  the  disk  revolves  at  100  revolutions  per  minute. 
When  driving  by  power  the  pinion  R  is  removed,  so  that  the 
wheel  and  crank  may  remain  at  rest.  The  jig  which  Mr.  Vezin 
had  made  for  the  author  was  provided  with  three  screen-boxes, 
as  follows  :  4^-  inches  deep,  2O-mesh  cloth,  openings  0.039  mcn  > 
3^  inches  deep,  3O-mesh  cloth,openings  0.024  inch;  3  inches  deep, 
6o-mesh  cloth,  openings  o.oio  inch.  If  it  is  desirable  to  increase 
the  depth  of  the  bed,  it  can  be  done  by  fitting  a  small  tail- 
board at  the  discharge  end. 

When  jigging  screen-sized  material,    the   separation  takes 


424 


APPENDIX  F. 


—  =0.  - 


place  in  the  upward  stream,  in  still  water  or  in  a  slow,  down- 
ward stream  ;  hence  water  must  be  supplied  under  the  plunger. 
This  is  accomplished  by  carrying  a  stream  to 
the  plunger  compartment  and  maintaining 
the  water  in  this  compartment  at  a  higher 
level  than  that  in  the  jig  compartment.  When 
water-sorted  material  is  jigged,  the  separation 
takes  place  in  the  downward  stream  ;  hence 
no  water  is  admitted  in  the  plunger  side,  but 
it  is  allowed  to  flow  in  with  the  ore  on  the 
feed-hopper.  The  feed-hopper  has  a  groove 
in  which  a  bit  of  rubber  packing  can  be 
slipped  under  the  inclined  bottom,  so  as  to 
contract  the  opening  and  prevent  the  water 
from  stirring  up  the  ore  as  it  falls  upon  the 
water  and  ore  in  the  screen.  When  greater 
suction  is  desired  the  ^--inch  bib-cock  in  the 
rear  can  be  partially  opened.  The  finer 
screens  are  provided  with  a  stay-box,  so  as 
to  jig  under  water  if  desired.  Place  a  plug 
from  above  in  the  discharge  of  the  stay-box, 
and  open  intermittently,  or  provide  the  plug  with  a  side-open- 
ing, to  allow  a  continuous  discharge. 

The  number  of  revolutions  and  the  length  of  stroke  are 
largely  a  matter  of  experiment.  Each  different  size  can  be 
experimented  with  until  these  points  are  determined,  when  the 
ore,  concentrates,  and  tailings  can  be  mixed  together  and  the 
test  can  then  be  made  under  the  proper  conditions.  As  a 
general  rule  the  total  throw  should  be  two  and  a  half  to  three 
times  the  diameter  of  the  grains  of  ore  so  as  to  separate  the 
particles  sufficiently  to  enable  them  to  arrange  themselves  ac- 
cording to  their  specific  gravities.  The  speed  must  be  suffi- 
cient to  raise  them.  The  greater  the  throw  the  less  the  speed, 
and  vice  versa.  The  following  are  recommended  when  treat- 
ing an  ore  containing  iron  pyrites  and  gangue,  the  gangue  be- 
ing essentially  quartz  and  feldspar  : 


FIG  6 


APPENDIX  F. 


425 


Sizes. 

Stroke  in  Inches. 

Revolutions 
per  Minute. 

Depth  of  Bed 
in  Inches. 

Mesh  per 
Linear  Inch. 

Diameter  in 
Inches. 

X'  ~  4  mesh. 
4-6 
6  -10 
10  -14 

14   -20 
20   -30 

ist  water  size 
2d  water  size 

0.250-0.157 
o.  157-0.110 
o.  110-0.079 
0.079-0.055 
0.055-0.039 
0.039-0.024 

I 

X 

% 
# 

5/i6 
3/i6 

3/16 

3/16-1/8 

1  60 
160 
1  60 
180 
200 
230 
290 
290-310 

3 
3 
3 
3 

2 
2 
2 

2 

The  concentrates  are  removed  from  the  sieve  by  skimming 
with  a  straight  piece  of  tin  about  eight  inches  in  length,  slightly 
narrower  than  the  sieve-box  and  bent  at  a  right  angle  at  one 
end.  The  straight  piece  is  used  for  skimming  and  the  right- 
angled  piece  for  removing  the  concentrates  from  the  screen. 

The  Richards  sorting-tube  *  illustrated  in  Fig.  6,  was  de- 
signed by  Prof.  Robert  H.  Richards  of  the  Massachusetts  In- 
stitute of  Technology  to  obtain  experimental  data  on  water 
sorting  in  upward  currents.  It  is  a  convenient  laboratory  sub- 
stitute for  the  spitz-lutte  or  hydraulic  classifier  of  the  mill. 
Hydraulic  water  is  fed  at  e,  at  a  constant  rate,  admitted  by  a 
dial-cock  at  constant  pressure,  guaranteed  by  an  overflow  col- 
umn pipe  to  give  a  constant  head.  This  passes  up  and  over- 
flows at  i  at  any  desired  speed.  The  fine  ore  is  fed  at  a,  in 
small  quantities  at  a  time.  The  grains  become  subject  to  the 
action  of  the  current  at  b.  If  they  are  light  enough  to  rise  in 
the  current  flowing  at  any  given  time  they  are  discharged  at  i. 
If  heavy  enough  to  fall,  they  pass  down  to  the  bulb^-.  A  ro- 
tary motion  is  given  to  the  water  in  d,  to  prevent  a  downward 
current  on  one  side  and  an  excess  of  upward  current  on  the 
other.  Two  products  are  obtained  at  each  operation,  over- 
flow grains  at  i  and  settled  grains  at  g.  The  overflow  from  i 
is  retained  for  subsequent  treatment,  that  is,  further  water 


*  Trans.  American  Institute  of  Mining  Engineers,  Vol.  XXVII. 


426 


APPENDIX  F. 


sorting  with  a  different  upward  current.  By  varying  the 
velocity  of  the  upward  current  at  each  operation,  a  number  of 
water-sorted  products  are  obtained.  The  various  minerals 
contained  in  each  of  these  products  may  then  be  separated  by 
jigging  (for  the  coarser  sizes)  and  vanning  (for  the  finer  sizes). 
The  method  of  calculating  and  tabulating  results  is  illus- 
trated in  the  following  table,  the  ore  being  iron  pyrites  with  a 
quartz  and  feldspar  gangue  : 


Assay  per 

Percentage 

Weight 

ton  2000  Ibs. 

saved. 

Avoir. 

Gold. 
Oz. 

Silver. 
Oz. 

Gold. 

Silver. 

Through  4-  and  over  8-mesh  jiff  concentrates  
Through  8-  and  over  ic-mesh  jig  concentrates  
Through  10-  and  over  2o-mesh  jig  concentrates  

1.91 

1.52 
0.85 

5-50 
5-9° 

15-0 
1  8.0 

24.0 

30.01 

25.62 
14.81 

19.1 
18.2 
13-6 

Through  20-  and  over  3o-mesh  jig  concentrates  ..  . 
First-water-size  concentrates  

0-45 

6.50 
8.00 

35-o 

8.36 

J°-5 
6.5 

Second-water-size  concentrates  from  vanning  

0.13 

9.80 

SO.Q 

^.64 

4-3 

Third-water-size  concentrates  from  vanning  

O.IO 

11.00 

68.0 

3-i4 

4-5 

5.20 

91.08 

76.7 

Amalgamation  Tests. — As  stamp-milling  and  amalgamation 
is  the  cheapest  of  all  processes  for  the  extraction  of  gold  from 
ore,  it  is  the  method  most  universally  adopted.  Unfortunately 
amalgamation  only  saves  such  gold  as  is  metallic  and  bright. 
After  the  upper  oxidized  part  of  our  gold  deposits  is  passed 
the  character  of  the  ore  changes  to  sulphides,  and  sometimes 
tellurides  ;  in  which  case  only  a  portion,  or  none,  of  the  gold  is 
in  a  state  so  that  it  can  be  saved  by  amalgamation.  Hence 
stamp-milling  is  frequently  followed  by  concentration  to  save 
the  gold  contained  in  the  sulphides  and  other  minerals.  In 
certain  cases  the  concentration  process  is  first  adopted,  and  the 
tailings  from  concentration  are  recrushed  and  treated  by  amal- 
gamation for  the  extraction  of  the  free  gold  which  has  not 
been  caught  by  concentration. 

The  most  satisfactory  method  of  testing  an  ore  to  deter- 
mine whether  its  gold  contents  can  be  saved  by  amalgama- 


APPENDIX  F.  427 

tion  is  to  ship  several  tons,  the  larger  the  quantity  the  better, 
to  some  mill  and  have  an  actual  working  test  made.  How- 
ever, this  is  not  always  feasible,  and 
laboratory  tests  frequently  have  to 
be  made.  These  laboratory  tests  on 
small  quantities  of  ore  are  also  some- 
times of  considerable  value  in  con- 
nection with  the  concentrating  tests 
previously  described. 

For   testing  samples   of   several 

hundred  pounds  by  amalgamation, 
FIG.  7.    CLEAN-UP  PAN.  the    laboratory   pan    or   the    «  dean. 

up  "  pan  of  the  mill,  shown  in  Fig.  7,  is  extremely  useful,  and 
the  results  of  tests,  made  by  this  apparatus,  should  be  closely 
duplicated  by  the  commercial  results  obtained  in  a  mill.  How- 
ever, such  apparatus  is  not  always  obtainable,  and  tests  on 
small  quantities,  with  the  aid  of  simple  apparatus,  may  be  re- 
quired. 

For  testing  small  quantities  of  ore  to  determine  the  per- 
centages of  gold  and  silver  which  can  be  extracted  by  amalga- 
mation the  reader  is  referred  to  Chapter  IX  of  Part  III. 


APPENDIX  G. 


THE  CALCULATION    OF   COPPER    MATTE    BLAST- 
FURNACE CHARGES. 

THIS  appendix  is  added  as  a  supplement  to  Chapter  III  of 
Part  IV.  The  problem  is  not  simple,  owing  to  the  continually 
varying  conditions  and  the  many  different  points  which  have  to 
be  considered,  the  most  important  being  as  follows : 

First. — The  charge  must  be  calculated  so  as  to  produce 
a  slag  which  will  be  good  both  from  a  metallurgical  and  an 
economic  standpoint.  A  good  metallurgical  slag  is  one  which 
is  fusible,  is  adapted  to  the  ores  to  be  smelted,  should  keep  the 
furnace  in  good  condition,  should  allow  a  good  separation 
of  the  matte,  and  hence  should  have  as  low  a  specific  gravity  as 
possible ;  should  be  low  in  both  copper  and  silver,  and  should 
usually  permit  of  a  high  degree  of  concentration  of  the  copper 
into  the  matte.  An  economic  slag  is  one  which  will  fulfil  the 
above  conditions  and  at  the  same  time  allow  an  economic  mix- 
ture of  the  ores  to  be  treated  so  that  a  minimum  amount 
of  costly  fuel  and  flux  will  be  required.  The  addition  of  flux 
to  the  furnace-charge  not  only  increases  the  smelting  cost, 
as  for  each  pound  of  flux  required  one  pound  less  of  ore  can  be 
treated,  thus  involving  an  additional  labor  and  fuel  expense  for 
the  ore  smelted,  but  it  diminishes  the  available  capacity  of  the 

428 


APPENDIX  G.  429 

In  copper  matte  smelting  the  percentage  composition  of  the 
slag  is  not  of  the  same  importance  as  in  lead  smelting,  where 
the  metallurgist  is  restricted  to  certain  type  slags  of  fixed 
chemical  composition.  The  lead  smelter  must  adhere  to  these 
types,  which  have  been  well  established,  in  order  that  eco- 
nomical work  may  result.  The  copper  metallurgist  is  simply 
restricted  within  rather  wide  limits  as  regards  the  percentages 
of  slag-producing  elements  which  may  be  present.  While  the 
type  slags  of  the  lead  smelter  may  be  used  in  copper  smelting, 
they  are  generally  uneconomical,  as  they  are  quite  basic  and 
require  a  large  amount  of  flux  for  their  production.  They 
fulfil  all  the  requirements  of  a  good  metallurgical  slag,  but 
in  most  localities  cannot  be  produced  without  the  addition  of 
considerable  limestone,  and  possibly  other  fluxes,  to  the  charge. 

The  limits  of  the  principal  slag  constituents  in  copper  matte 
smelting  may  be  stated  as  follows  : 

SiO,  ................................  26  to 

A12O3  ...............................     o  to  2 

FeO  ................................  18  to 

CaO  ............  ...................     oto 

ZnO  ................................     o  to 


In  this  table  MnO  is  regarded  as  replacing  FeO,  and  BaO 
and  MgO  as  replacing  CaO.  Manganese  replaces  iron  and 
renders  the  slag  extremely  fusible.  It  was  formerly  considered 
as  having  a  tendency  to  carry  silver  into  the  slag,  and  conse- 
quently as  detrimental.  lies  *  and  Church,f  however,  have 
demonstrated  that  it  is  not  detrimental,  and  Church  claims  to 
have  made  slags  containing  over  43$  MnO  which  were  remark- 
ably low  in  silver  (0.5  oz.  per  ton). 

The  presence  of  MgO  and  BaO  in  copper  slags  is  not  as 
objectionable  as  in  lead  slags  where  under  4$  of  either  oxide  is 

*  School  of  Mines  Quarterly,  Vol.  V,  p.  217. 

f  Trans.   Am.  Inst.  M.  E.,  Vol.  XV,   p.  612.      School  of  Mines  Quar- 
terly, Vol.  V,  p.  322. 


43°  APPENDIX  G. 

generally  regarded  as  the  safe  limit.  Copper  matte  slags  have 
been  successfully  run  with  as  much  as  12$  of  these  oxides. 
The  presence  of  BaO  is  objectionable,  as  it  raises  the  specific 
gravity  of  the  slag.  The  presence  of  zinc  is  objectionable 
in  both  lead  and  copper  smelting,  as  it  has  a  tendency  to  render 
the  slag  thick  and  infusible  and  consequently  increases  the  slag 
loss  in  valuable  metals.  It  also  has  a  marked  tendency  to 
increase  the  loss  of  silver  by  volatilization  during  the  roasting 
or  smelting  operations.  In  lead  smelting  13$  of  ZnO  in  the 
slag  may  be  regarded  as  the  maximum  limit,  but  in  copper 
smelting  slightly  higher  limits  have  been  reached.  All  slags 
contain  other  constituents,  as  NaQO,  K2O,  PbO,  CuaS,  CaS,  etc., 
which  are  generally  present  in  small  quantities,  so  that  the  sum 
of  the  SiO3,  FeO,  MnO,  CaO,  ZnO  and  A12O3  may  be  taken  as 
forming  from  90  to  95$  of  the  slag,  except  when  much  MgO  or 
BaO  is  present.  The  action  of  alumina  in  these  slags  has  been 
the  subject  of  much  speculation  and  discussion,  and  more  exact 
information  on  this  important  question  is  needed.  In  the 
highly  ferruginous  slags  of  the  lead  and  copper  smelter,  alumina 
usually  plays  the  part  of  an  acid,  but  slags  are  occasionally  en- 
countered in  which  the  alumina  is  present  as  a  base. 

The  specific  gravity  of  the  slag  is  an  important  point.  The 
loss  of  silver  and  copper  in  the  slag  will  depend  largely  upon 
the  difference  in  specific  gravity  of  the  matte  and  slag.  The 
specific  gravity  of  the  ordinary  matte  may  be  stated  as  from 
5.0  to  5.5,  whilst  that  of  the  slag  is  from  3.5  to  3.75.  It  is 
essential  that  a  considerable  difference  in  specific  gravity  (1.75 
about)  should  exist  between  the  matte  and  slag  in  order  that  a 
good  separation  may  be  effected.  Of  course,  the  greater  the 
difference,  other  things  being  equal,  the  more  perfect  the 
separation. 

Second.  The  furnace  charges  must  be  arranged  so  as  to  use 
up  the  ores  on  hand  and  the  daily  supply  in  about  the  propor- 
tions in  which  they  exist.  This  requires  that  the  ore  buyer,  or 
mine  superintendent,  and  the  metallurgist  should  keep  in 


APPENDIX  G.  431 

touch  with  each  other  and  be  familiar  with  the  requirements  of 
each. 

Third.  The  charges  must  be  calculated,  as  near  as  possi- 
ble, so  that  the  resulting  matte  will  be  of  the  proper  grade  for 
shipment  or  for  its  further  metallurgical  treatment  at  the 
works.  This  is  frequently  a  question  of  great  importance,  as, 
for  example,  suppose  the  matte  is  to  be  treated  for  blister 
copper  by  bessemerizing  at  the  works.  In  the  United  States 
it  has  not  so  far  proven  profitable  to  bessemerize  mattes  con- 
taining much  less  than  50$  copper.  When  the  matte  is 
shipped  to  a  distant  refining- works  for  further  treatment  the 
freight  and  refining  charges  are  items  which  cannot  be  disre- 
garded in  the  calculation  of  what  will  be  the  most  profitable 
grade  of  matte  to  produce.  The  percentage  of  copper  in  the 
furnace  charge  and  the  fall  of  matte  will  also  have  an  influence 
on  the  loss  of  silver  and  copper  in  the  smelting  operation. 

Fourth.  The  amount  of  sulphur,  arsenic,  and  antimony 
which  will  be  volatilized  in  smelting  is  of  the  greatest  impor- 
tance, and  upon  this  many  of  the  other  questions  will  depend 
to  a  large  extent.  This  has  a  direct  influence  on  the  rate  of 
concentration,  the  grade  of  the  matte,  and  the  consumption  of 
fuel,  all  questions  of  vital  importance.  This  facotr  is  ex- 
tremely variable,  the  amount  volatilized  being  from  8.^  in 
ordinary  matte  smelting  to  probably  90$  in  true  pyritic  smelt- 
ing. It  depends  upon  the  construction  and  operation  of  the 
furnace  and  upon  the  physical  and  mineralogical  character  of 
the  ores.  Depending  upon  so  many  variable  considerations,  it 
is  impossible  to  formulate  any  rule  which  will  serve  as  more 
than  a  guide  in  the  calculation.  A  safe  rule  can  only  be 
arrived  at  after  the  furnace  has  been  in  operation  for  some 
time  and  after  numerous  experiments  have  been  made.  Even 
then  no  absolute  rule  can  be  formulated,  as  conditions  will 
necessarily  vary  from  time  to  time.  In  connection  with  this 
question  it  should  be  remembered  that  for  pyritic  smelting 
the  amount  of  sulphur  consumed  by  oxidation  must  be  large. 


43 2  APPENDIX   G. 

True  pyritic  smelting  requires  at  least  65$  of  pyrites,  or  equiv- 
alent sulphides  or  arsenides,  on  the  furnace  charge  in  order 
that  sufficient  heat  may  be  generated  to  smelt  the  mixture.  It 
is  true  that  partial  pyritic  smelting  is  successfully  carried  on 
with  a  smaller  percentage  of  pyrites,  using  carbonaceous  fuel 
in  the  furnace,  and  limestone  as  a  flux  to  supply  the  deficiency 
in  basic  elements  on  the  charge. 

Fifth.  The  character,  or  chemical  composition,  of  the  re- 
sulting matte  must  be  considered.  This  will  depend  upon  the 
mineralogical  character  of  the  ores,  the  volatilization  of  sul- 
phur, arsenic,  antimony,  zinc,  and  lead,  the  operation  of  the 
furnace  and  the  character  of  the  resulting  slag.  As  these  are 
all  variable  no  exact  rule  can  be  formulated  for  the  determina- 
tion of  this  question.  Until  the  works  have  been  in  operation 
for  a  sufficient  time,  so  that  the  question  can  be  settled  by 
frequent  analyses  of  the  matte,  the  following  rule  will  serve  as 
a  guide : 

1.  From  the  total  S,  As  and  Sb  on  the  charge,  deduct  such 
amount   as  will   probably   be    volatilized   (in    ordinary   matte 
smelting  this  may  be  taken  as  10$).     The  balance  is  to  be  con- 
sidered as  S,  etc.,  available  for  matte. 

2.  Calculate  all  of  the  copper  present  to  Cu2S. 

3.  Calculate  three-quarters  of  the  lead  present  to  PbS. 

4.  Calculate  one-half  of  the  zinc  present  to  ZnS. 

5.  Calculate  the  remainder  of  the  available  sulphur  to  FeS. 
These  sulphides  will  usually  constitute  from  90  to  95$  of 

the  matte.  The  remainder  will  be  slag  mechanically  mixed 
with  the  matte,  probably  metallic  iron,  and  other  sulphides, 
arsenides  and  antimony  compounds.  The  matte  may  also  con- 
tain sulphides  and  arsenides  other  than  the  simple  ones 
enumerated.  The  true  composition  of  matte  has  never  been 
accurately  determined,  and  a  thorough  investigation  of  the 
subject  would  be  of  great  benefit  to  modern  metallurgy. 
The  calculation  is  illustrated  by  the  following  example : 


APPENDIX  G. 


433 


ANALYSIS   OF   ROASTED    ORE. 


SiO, 
Fe.. 
Cu.. 
Zn.. 
Pb.. 
S.. 


7% 


Assuming  that  iof0  of  the  sulphur  will  be  volatilized,  we 
have  6.3  parts  of  sulphur  available  for  matte  in  each  100  parts 
of  ore. 


Mol.  Wt.  Cu, 

126 
At.  Wt.  Pb 

207 
At.  Wt.  Zn 

65 


Mol.  Wt.  CuaS  =  Parts  Cu 
158  10 

Mol.  Wt.  PbS    =  |  Parts  Pb 
239  =         2.25 

Mol.  Wt.  ZnS  =  £  Parts  Zn 
97  =         2.25 


Parts  Cu,S. 

12.54. 
Parts  PbS. 

2.59. 
Parts  ZnS. 

2.35- 


The  sum  of  these  sulphides  is  17.48  parts.  This,  less  the 
sum  of  the  metals  (14.5),  leaves  2.98  parts  of  sulphur,  which 
combine  with  the  Cu,  Pb  and  Zn,  leaving  (6.3  —  2.98)  3.32 
parts  of  sulphur  to  combine  with  the  iron. 

At.  Wt.  S  :  Mol.  Wt.  FeS  =  Parts  S  :  Parts  FeS. 
32       :  88  =      3.32     :        9.13. 

If  we  assume  that  the  Cu,S,  FeS,  PbS  and  ZnS  constitute 
90$  of  the  matte,  for  the  parts  of  matte  produced,  we  have 


=  29.5 


and  for  the  percentage  of  copper  in  the  matte 
29.5  :  10  =  100  :  *;  *  =  33-9^- 

This  figure  is  too  high,  as  no  allowance  has  been  made  for 
loss  of  copper  in  the  slag. 


434  APPENDIX   G. 

The  next  step  in  the  calculation  is  to  determine  whether 
sufficient  iron  is  present  to  form  a  good  slag.  For  iron  avail- 
able for  slag  we  have  46  —  (9.13  —  3.32)  or  40.19  parts,  which 
is  equal  to  51.67  parts  FeO.  If  we  assume  that  the  SiO3  and 
FeO  constitute  90$  of  the  slag,  we  have 

25  +  51-67  =  g^  ig 
Its  composition  is  as  follows  : 


This  shows  the  resulting  slag  to  be  somewhat  high  in  iron 
and  low  in  silica.  This  might  be  obviated  by  leaving  more 
sulphur  in  the  roasted  ore,  which  would  result  in  a  larger 
amount  of  iron  going  into  the  matte  ;  or,  should  silicious  ores 
be  available,  sufficient  silica  in  the  form  of  ore  could  be  added 
to  produce  a  slag  of  the  proper  composition.  The  necessary 
fuel  to  be  added  to  the  charge  will  also  supply  some  of  the 
deficient  silica. 

Sixth.  The  furnace  charge  should  have  the  proper  weight, 
which  will  depend  principally  upon  the  size  of  the  furnace  and 
somewhat  upon  the  character  of  the  ores.  The  weight  of  the 
charge  will  have  a  direct  bearing  upon  the  practical  working  of 
the  furnace.  It  will  vary  from  2000  to  4000  pounds,  accord- 
ing to  the  conditions,  the  proper  weight  having  to  be  deter- 
mined by  actual  experiment  in  each  individual  case. 

Seventh.  The  amount  of  fuel  to  be  added  to  the  charge  and 
the  amount  and  composition  of  its  ash  are  important  points. 
The  amount  necessary  will  depend  upon  its  character,  the 
character  of  the  ores,  the  composition  of  the  slag,  and  the 
operation  of  the  furnace.  In  ordinary  matte  smelting,  where 
only  a  small  percentage  of  the  sulphur  present  is  volatilized, 
from  IO  to  15$  of  good  coke  will  be  required.  By  fuel  per- 


APPENDIX   G.  435 

centage  is  understood  a  percentage  of  the  ore  and  flux  charge. 
This  estimate  is  based  upon  a  good,  firm,  porous  coke  contain- 
ing about  I2fc  ash.  As  the  percentage  of  ash  increases,  or  the 
quality  of  the  coke  deteriorates,  the  amount  used  must  be 
increased.  As  the  amount  of  sulphur,  arsenic,  or  antimony 
volatilized  increases,  the  percentage  of  carbonaceous  fuel  re- 
quired decreases,  until  in  the  case  of  true  pyritic  smelting  no 
carbonaceous  fuel  is  added  to  the  charge,  the  combustion  of 
the  sulphur,  arsenic,  etc.,  together  with  the  hot  blast  intro- 
duced at  the  tuyeres,  supplying  the  necessary  heat-units. 

Eighth.  The  loss  of  gold,  silver,  and  copper  in  the  smelting 
operation  demands  consideration.  These  losses  will  vary 
according  to  the  grade  and  character  of  the  ores  and  matte, 
the  character  of  the  slag,  the  operation  of  the  furnace,  and  the 
facilities  provided  for  the  collection  of  flue-dust  and  fume.  In 
true  pyritic  smelting  (the  operation  being  one  of  oxidation)  the 
losses  will  be  greater  than  in  ordinary  matte  smelting,  where 
the  action  is  reduction.  The  presence  of  copper  in  the  charge 
will  have  a  marked  effect  on  the  gold  and  silver  losses,  even 
small  amounts  having  a  marked  tendency  to  increase  the  con- 
centration of  the  precious  metals  in  the  matte.  In  ordinary 
matte  smelting  the  loss  in  gold  should  be  practically  nil,  and 
the  silver  loss  should  not  exceed  5$  of  the  assay  value  of  the 
ore.  The  copper  loss  will  depend  principally  upon  the  amount 
and  character  of  the  slag  produced.  With  ordinary  mattes, 
containing  as  much  as  40$  copper,  a  good  slag  should  not  con- 
tain over  0.6$  copper.  Under  exceptional  commercial  condi- 
tions, it  may  prove  profitable  to  make  slags  assaying  consider- 
ably higher ;  but  in  good  work,  and  under  ordinary  conditions, 
the  slags  rarely  exceed  0.5$.  The  amount  of  zinc  present  may 
largely  affect  the  gold  and  silver  losses.  The  zinc  oxide  which 
is  volatilized  invariably  carries  off  mechanically  both  gold  and 
silver.  These  losses  may  be  reduced  by  the  introduction  of 
proper  dust-  and  fume-saving  apparatus,  but  cannot  be  entirely 
obviated.  Zinc  also  makes  bad  slags,  and  hence  increases  the 
loss  of  gold,  silver,  and  copper  in  the  slag.  The  production  of 


436 


APPENDIX   G. 


a  matte  of  as  high,  and  a  slag  of  as  low,  a  specific  gravity  as 
possible,  and  the  use  of  efficient  settling  and  separating  appara- 
tus will  also  largely  determine  the  losses. 

The  calculation  of  the  charge  is  illustrated  by  the  following 
examples : 

Example  No.  I.  The  works  have  a  smelting  capacity  of  300 
tons  per  24  hours.  Ore  A,  which  is  roasted,  is  practically 
unlimited  in  quantity,  coming  from  mines  belonging  to  the 
smelting  company.  Ore  B  can  be  purchased  to  the  extent  of 
75  tons  per  day,  and  at  a  fair  profit.  The  matte  is  shipped  and 
sold  to  refiners.  The  assay  of  the  ores  is  as  follows : 


Ore 

SiOa£ 

Fe* 

Cu# 

Pb* 

Zn£ 

S£ 

A1308# 

CaO* 

Ag. 
Ozs.  per  ton. 

Au. 
Ozs.  per  ton. 

A 

25 

46 

TO 

3 

3 

7 

15 

0-5 

B 

50 

5 

3 

2 

10 

12 

50 

O.I 

Coke 

6 

i 

(as 

h  10 

*) 

2 

I 

Assuming  that  we  will  smelt  about  250  tons  of  ore  A  and 
50  tons  of  ore  B  per  day,  and  want  a  furnace  charge  of  about 
3000  pounds,  we  have,  for  pounds  of  each  constituent  of  the 
charge : 


Ore. 

Si02 
IDS. 

Fe 
Ibs. 

Cu 

Ibs. 

Pb 

Ibs. 

Zn 
Ibs. 

S 
Ibs. 

A1.0, 
Ibs. 

CaO 

Ibs. 

Ozs. 

Ag 

Ozs. 
Au 

Pounds 
per  charge. 

A 

625 

1150 

250 

75 

75 

175 

18.75 

0.625 

25OO 

B 

250 

25 

15 

10 

50 

60 

12.50 

0.025 

500 

Coke 

22 

4 

7 

4 

360 

Total 

897 

1179 

265 

75 

75 

185 

57 

64 

31.25 

0.650 

Assuming  that  io#  of  the  sulphur  is  volatilized,  we  have 
166.5  pounds  of  sulphur  available  for  matte.  Calculating  the 
copper  to  Cu,S,  two-thirds  of  the  lead  to  PbS  and  one-half  of 
the  zinc  to  ZnS  we  have 


APPENDIX  G.  437 

126  :  158  =  265     :  x  •  x  —  332.3  Ibs.  Cu,S 

207  :  239  =     50     \y\y-     57.7  Ibs.  PbS 

65:    97=    37-5:*;*=    55-9lbs-ZnS 

352.5  445-9 

and  445.9  —  352.5  ==  93.4  pounds  of  sulphur  combining  with 
the  Cu,  Pb,  and  Zn.  This  leaves  (166.5  —  93.4)  73.1  pounds  of 
sulphur  to  be  calculated  to  FeS.  We  have 

32  :  88  =  73. 1  :/ ;  /  =  201  Ibs.  FeS. 

Hence  for  iron  available  for  slag  we  have  1179  —  (201  —73.1)  = 
1051  pounds.  As  some  zinc,  lead,  copper,  and  small  amounts 
of  other  elements  which  are  usually  present,  pass  into  the  slag 
the  SiO2,  FeO,  CaO  and  A1,O3  will  usually  form  about  93  %  of 
the  slag  constituents.  Hence  we  have  for  the  pounds  of  slag 
produced  per  charge  : 

897+  1051  X  |+57 +  64 

=  2547. 

0-93 

The  composition  of  the  slag  will  be  as  follows : 

897  X  i  QQ 
2547 

!f|          ^5  =  S3.o*F«o. 
*£F    ="*A'-°- 

64  X  ioo 


2547 


=  2.6  %  CaO. 


This  slag  should  run  well  and  give  a  good  separation  of 
matte,  but  is  somewhat  high  in  iron  and  low  in  silica.  Should 
a  more  acid  slag  be  desirable  it  may  be  obtained  by  slightly 
increasing  the  amount  of  ore  B. 

Before  calculating  the  amount  and  the  composition  of  the 
resulting  matte  it  is  necessary  to  make  allowance  for  the  loss  of 


438 


APPENDIX  G. 


copper  in  the  slag.  Assuming  the  resulting  slag  will  assay 
0.4$  copper,  we  have  10.2  pounds  of  copper  to  deduct  from 
the  total  copper  present,  the  remainder  being  that  going  to  form 
matte.  This  is  equivalent  to  12.7  pounds  of  CuaS.  If  we 
assume  that  the  Cu2S,  PbS,  ZnS,  and  FeS  form  93$  of  the 
matte,  we  have 

(445-9^-  1^.7)  +  201  =  682  lbs>  of 


The  percentage  of  copper  in  the  matte  is 


(265  --  10.2)  X  ioo 
682 


37- 


Allowing  for  a  smelting  loss  of  5$   silver   and  \<f>  gold,  we 
have,  for  the  assay  of  the  matte : 

29.68/5    X    2OOO 


682 


=  87.06  ozs.  Ag  per  ton. 


0.6435    X    2000 

6g2  =     1.88  ozs.  Au  per  ton. 

Example  No.  2.  We  have  the  following  ores  to  smelt,  the 
capacity  of  the  works  being  300  tons  per  day.  Ore  A  is  pur- 
chased at  a  small  profit  and  stall-roasted.  Ores  B  and  C  are 
purchased  at  a  good  profit,  and  whilst  ore  C  is  a  heavy  sulphide, 
the  local  conditions  are  such  that  it  would  be  inadvisable  to 
roast  it.  The  matte  is  shipped  and  sold  to  refiners.  The  ores 
assay  as  follows : 


Ore 

A 
B 

SiOa* 

Fe* 

Cu* 

s* 

CaO* 

Pb^ 

Zn# 

Ag. 
Ozs.  per  ton. 

Au. 
Ozs.  per  ton. 

10 

55 

12 

7 

5 

0-3 

go 

5 

I 

i5 

1.0 

C 

15 

25 

5 

35 

5 

4 

6 

20 

0-5 

Assuming  that  we  smelt  200  tons  of  ore  A,  50  tons  of  ore  B, 
and  50  tons  of  ore  C  per  day  and  wish  about  3000  pounds  on  the 


APPENDIX  G. 


439 


furnace  charge,  we  have,  for  the  pounds  of  the  different  con- 
stituents on  the  charge  : 


Ore 

Si02 
Ibs. 

Fe 
Ibs. 

Cu 

Ibs. 

S 

Ibs. 

CaO 

Ibs. 

Pb 

Ibs. 

Zn 

Ibs. 

Ag 
Ozs. 

Au 
Ozs. 

Pounds  per 
charge. 

A 

200 

1  100 

240 

140 

5-00 

0.300 

2OOO 

B 

450 

25 

5 

3-75 

0.250 

500 

C 

75 

125 

25 

175 

25 

2O 

30 

5-oo 
13-75 

o.  125 

500 

Total 

725 

I25O 

270 

315 

25 

2O 

30 

0.675 

3000 

Calculating  the  Cu  to  Cu2S,  one-half  the  Zn  to  ZnS,  two- 
thirds  of  the  Pb  to  PbS,  and  assuming  that  8$  of  the  sulphur 
is  available  for  matte,  we  have : 

Cu2S  pounds 338.5 

PbS        "       15.3 

ZnS        " 22.4 

FeS        "  478.8 


855.0 

Which  leaves  1215  pounds  of  FeO  available  for  slag.  If  the 
SiO2,  FeO,  and  CaO  form  90$  of  the  slag,  we  will  have  2183 
pounds  of  slag  produced  per  charge  and  its  composition  will  be : 

SiO, 33.2^ 

FeO 55.6$ 

CaO 1.20 

This  slag  is  slightly  basic,  hence  the  weight  of  ore  B  might 
be  increased  to  advantage.  Using  700  pounds  of  ore  B,  we 
will  have  2397  pounds  of  slag  produced  per  charge,  and  its 
composition  will  be : 

SiO2 37-8$ 

FeO 5I.I0 

CaO 1. 10 

If  the  slag  assays  0.5$  copper  and  the  CuaS,  PbS,  ZnS,  and 
FeS  constitute  93$  of  the  .matte,  the  percentage  of  copper  in 


44°  APPENDIX   G. 

the  matte  should  be  27.4.  It  should  assay  32.6  ounces  silver 
and  1.72  ounces  gold  per  ton,  assuming  a  5$  silver  loss  and  no 
loss  in  gold. 

Example  No.  j.  It  is  desired  to  erect  a  plant  for  the  con- 
centration of  the  copper  and  silver  contained  in  an  ore  of  the 
composition  given  into  a  matte  for  shipment.  Upon  roasting 
at  a  cost  of  $i  per  ton  the  ore  yields  a  product  of  the  com- 
position shown.  With  coke  at  $8  per  ton  the  estimated  cost 
of  ordinary  matte  smelting  of  the  roasted  ore  is  $4  per  ton, 
and  the  estimated  cost  of  pyritic  smelting  of  the  raw  ore  is 
$3.25  per  ton.  Freight  to  the  refining-works  on  each  ton  of 
matte  is  $10.  Which  will  be  more  profitable,  ordinary  matte 
or  pyritic  smelting  ? 

Raw  Ore.     Roasted  Ore. 

SiOa 15    %  17.5* 

Fe 34    %  39.6$ 

Cu 4.1$  4.7$ 

CaO..... 3    %  3-5$ 

S 40    %  7    % 

Ag , 2OOZS.  23  ozs. 

One  ton  of  raw  ore  yields  1720  pounds  of  roasted  product. 
We  will  assume  that  in  ordinary  matte  smelting  90$  of  the 
sulphur  will  pass  into  the  matte,  while  in  pyritic  smelting  only 
20$  of  the  sulphur  is  available  for  matte.  Calculating  the 
charges  as  before  and  assuming  that  the  Cu,S  and  FeS  con- 
stitute 95$  of  ths  matte  and  that  the  SiO3,  FeO,  and  CaO  con- 
stitute 99$  of  the  slag,  we  have : 

Pyritic  Smelting.  Matte  Smelting. 

Matte  produced  per  ton  of  crude  ore,  511  pounds.  361  pounds. 

Slag             "             "               "       "      969       "  1092 

Copper  in  matte 15.2$  21.6$ 

Cost  of  smelting  per  ton  of  crude  ore,  $3.25  $3-44 

"     "  roasting        "               "         "       i.oo 

Freight  on  matte     "               "         "       2.55  1.82 


Total  cost $5.80  $6.26 


APPENDIX   G.  441 

The  slags  will  have  the  following  composition  : 

From  From 

Pyritic  Smelting.        Matte  Smelting. 

SiO, 30.9$  27.4^ 

FeO 57.9^  62.0^ 

CaO 6.2f0  5.6$ 

The  slag  resulting  from  pyritic  smelting  is  somewhat  the 
best  and  should  give  a  better  separation  of  matte  than  that 
resulting  from  the  matte-smelting  operation.  Taking  this  fact, 
and  also  the  loss  of  silver  in  roasting,  into  consideration,  the 
total  losses  will  probably  be  about  the  same  by  either  opera- 
tion. With  such  an  ore,  under  the  conditions  given,  pyritic 
smelting  would  appear  to  be  the  cheapest  process.  However, 
the  difference  of  $0.46  per  ton  in  favor  of  pyritic  smelting 
would  probably  be  more  than  offset  by  the  refining  charges  on 
the  increased  amount  of  matte  and  in  consequence  of  its 
lower  grade. 


INDEX. 


A 

PAGE 

Absorbents  used  in  the  Analysis  of  Gases 272 

Absorption,  Determination  of  Carbonic  Acid  by no 

«•  •'  "Sulphurby 96,99 

J«  "  "  Water  by 120 

Acetate  of  Ammonium  (Solvent) 70 

"  Sodium  (Precipitant) 72 

Acetic  Acid  (Solvent) 70 

'"          "  ,  Analysis  of  Commercial 287 

Acid,  Citric  (Solvent) 70 

Acidimetry  and  Alkalimetry 282 

Acid,  Hydrochloric  (Solvent) 69 

"    ,  Hydrofluoric  (Flux) 67 

"    ,  Nitric  (Oxidizing  Reagent) 7* 

"    ,      "     (Solvent) 69 

es    ,  Oxalic  (Solvent) , 70 

*'    ,  Solutions,  Standard 282 

"    ,  Sulphuric  (Precipitant) 72 

"    ,         "         (Solvent) 69 

4 '   ,  Tartaric  (Solvent) 7° 

Acidity  of  Ores,  Tests  for  the 4°3 

Albuminoid  Ammonia  in  Water,  Determination  of 280 

Alexander's  Method  for  the  Determination  of  Lead 142 

Alkalies,  see  Potassium  and  Sodium. 

"         in  Water,  Determination  of 276 

Alkalimetry  and  Acidimetry 282 

Alkali  Solutions,  Standard 285 

Alumina,  Determination  of 181 

"          in  Iron  Ores,  Determination  of , 183 

"          "  Lead  Ores,  "  " 184 

443 


444  INDEX. 

IAGH 

Alumina  in  Limestones,  Clays,  etc.,  Determination  of 184 

"         "  Manganese  Ores,  " 184 

"Mattes,  "  " 184 

"        "  Natural  Phosphates,  "  " 304 

"Slags,  ••  " 184 

"SilverOres,  "  " 184 

"Water,  "  " 275 

Aluminium  (Precipitant) 73 

,  Analysis  of  Commercial 298 

,  Determination  of 181 

••  "  "  as  Alumina  182 

"  "  "  as  Phosphate 186 

' '  in  Commercial  Aluminium,  Determination  of 298 

*'•  Phosphate,  Composition  of 186 

"         ,  Test  for  (Blowpipe) 22 

"  "      "(Qualitative) 39 

Amalgamating-pan 427 

Amalgamation  Assay 260 

Ammonia  (Precipitant) 71 

(Solvent) 70 

in  Water,  Determination  of ,. . .  278 

Ammonium  Acetate  (Solvent) 70 

"  Carbonate  (Precipitant) 71 

"  Chloride  (Precipitant) 72 

"  Nitrate  (Oxidizing  Reagent) 75 

"  Oxalate  (Precipitant) 71 

"          Sulphide  (Precipitant) 71 

"  "        (Solvent) 70 

"        ,  Test  for  (Blowpipe) 22 

Analysis  of  Bleaching  Powder 289 

"        "  Coal  and  Coke 263 

"       "  Commercial  Acetic  Acid 287 

"        "  "  Caustic  Potash , 287 

Aluminium 298 

"       "  Gases 269 

"        "  Lead  and  Copper  Slags 307 

"        "  Natural  Phosphates , 300 

"       "  Water 274 

"  White-Lead , 291 

Antimony,  Determination  of 147 

in  Ores  containing  Iron  and  Lead,  Determination  of 150 

"  Oxidized  Ores,  Determination  of 149 

"  "  Refined  Copper,          "  " 413 

"  "  Sulphide  Ores,  "  " 149 

"         ,  Test  for  (Blowpipe) 23 

"  "      "     (Qualitative) 39 

Apparatus  and  Operations 49 


INDEX.  445 

PAGE 

Apparatus  for  the  Determination  of  Carbonic  Acid  by  Direct  Weight 117 

"           "      "               "               "  Sulphur  by  Absorption 95 

"           "      "  Rapid  Analysis  of  Gases 270 

Approximate  Analysis  of  Coal  and  Coke 263 

Aqueous  Vapor,  Table  showing  the  Tension  of 355 

Argol  (Flux) 68 

Arsenic,  Determination  of 144 

"        in  Refined  Copper,  Determination  of 413 

"      ,  Test  for  (Blowpipe) ' 23 

"             "      "(Qualitative) 39 

Assay,  Amalgamation 260 

' '      of  Base  Bullion 232 

"       "  Copper  Matte,  Special  Method  for 250 

"  Gold  and  Silver  Ores  (Crucible) 126 

"       "      "       "         "           "     (Scorification) 123 

«'       "      "       ««         "          "     containing  Metallic  Scales 258 

"      "     Bullion 246 

"       "  Silver  Bullion  by  Fire  Method 236 

"       M      "            "             "     Gay-Lussac  Method 240 

"       "      "            "            "     Volhard's          "       245 

"  Silver  Sulphides 252 

Assay-ton  Weights 51 

Atomic  Weights,  Table  of 354 

B 

Balances    51 

Barium,  Determination  of 224 

"      ,  Test  for  (Blowpipe) 24 

"  "     "    (Qualitative) 39 

Chloride  (Precipitant) , 70 

Base  Bullion  Assay  232 

"     ,  Sampling  of 14 

"          "       Special  Method  for  the  Assay  of  Impure 234 

Base  Metal  in  Gold  Bullion 246 

Beakers 61 

Bicarbonate  of  Soda  (Flux) 67 

Bichromate  of  Potassium  (Oxidizing  Reagent)  75 

Bismuth,  Determination  of 163 

"        in  Refined  Copper 413 

"     ,  Test  for  (Blowpipe) 24 

"      "(Qualitative) 40 

Bisulphate  of  Potassium  (Flux) 66 

Black  Flux 68 

"         "     Substitute..  ,     68 


446  INDEX. 


Blowpipe  Tests 22 

Borax  (Flux) 67 

Boron,  Test  for  (Blowpipe) 25 

"         "        "(Qualitative) 40 

Bromine  (Oxidizing   Reagent) 75 

' '       Reagent  in  Gas  Analysis , . .  272 

"     ,  Test  for  (Blowpipe) 25 

"           "       "  (Qualitative) 40 

Brunton's  Sampling  Apparatus 12 

Bunsen's  Method  for  the  Determination  of  Antimony 147 

Burettes 63 


C 

Cadmium,  Determination  of 166 

•'  "  "  Zinc  in  Ores  of 210 

"      ,  Test  for  (Blowpipe) 25 

"  "       "   (Qualitative) 40 

Calcium,  Determination  of 215 

"  "  in  Clays 217 

"  "  "  "Limestone 215 

"  "  "   "Natural  Phosphates 303 

"  "  "''Ores 217 

"  "  ""Slags 218 

"  "  ""Water 275 

"     ,  Test  for  (Blowpipe) 26 

"  "       "    (Qualitative) 41 

Calculation  of  Copper-matte  Blast-furnace  Charges 428 

"  "  Factors 323 

"  Formulae 324 

"  Percentage  Composition  from  Chemical  Formula 321 

from  Weight 321 

"  Lead  Blast-furnace  Charges 337 

"  Specific  Gravity 293 

"  the  Results  of  Analysis,  Table  of  Factors  for  the 357 

"       "  Indirect  Analysis 331 

"       "  the  Amalgamation  Assay 261 

"       "    "    Assay  of  an  Ore  containing  Metallic  Scales  259 

"       "    "    Analysis  of  Gases 332 

"  "    "          "       "    "    Assay  of  Gold  Bullion 248 

"       ""         "      "  Silver  Bullion 244 

"    "   Percentage  of  Extraction  in  the  Chlorination  Assay  of 

Gold  Ores 257 

"    "   Percentage  of  Extraction   in  the  Chlorination  Assay  of 

.  Silver  Ores 254 


INDEX.  447 

PAGE 

Calculation  of  the  Strength  of  the  Salt  Solution  used  in  the  Volumetric  As- 
say of  Silver  Bullion 242 

Calculations  involved  in  the  Use  of  Volumetric  Solutions 328 

Carbonate  of  Ammonium  (Precipitant) 71 

"         "  Potassium  (Flux) 66 

"  Soda  (Flux) , 66 

"         "      "      (Precipitant) 72 

Carbonic  Acid,  Determination  of 116 

"         "      in  Natural  Phosphates,  Determination  of 301 

"      Test  for  (Blowpipe) 26 

"         •'         "      "    (Qualitative) - 41 

Carbon,  Determination  of 106 

"         in  Coal  and  Coke,  Determination  of  Fixed 264 

"         Standards,  Eggerz's  Mixture  for 114 

Carnot's  Method  for  the  Determination  of  Antimony 148 

Casseroles , 61 

Characteristic  Blowpipe  Tests 22 

"             Qualitative  Tests 38 

Charcoal  (Reducing  Flux) 68 

Charges  for  Blast-furnaces,  Calculation  of 337 

Chlorate  of  Potassium  (Oxidizing  Reagent) 75 

Chloride  of  Ammonium  (Precipitant). 72 

"       ' '  Barium  (Precipitant) 70 

"       "  Silver  in  Ores,  Determination  of 254 

"  Tin  (Reagent) 74 

Chlorimetry 289 

Chlorination  Assay  of  Gold  Ores 256 

•«                 "       "Silver     " 254 

Chlorine  (Oxidizing  Reagent) 75 

"       Available  in  Bleaching-powder 289 

"       in  Water,  Determination  of 277 

"     ,  Test  for  (Blowpipe) 26 

"           "       "(Qualitative) t 41 

Chromium,  Determination  of 188 

"        ,  Test  for  (Blowpipe) 26 

"             "       "    (Quantitative) 41 

Citric  Acid  (Solvent) 70 

Classification  of  Coals 263 

Clays,  Determination  of  Alumina  in 184 

"                "                 "  Calcium  in 217 

"                "                 "  Iron  in 177 

"                "                 "  Magnesia  in 223 

"                "                 "  Silica  in  84 

Coal,  Analysis  of 263 

Cobalt,  Determination  of 211 


44$  INDEX. 


Cobalt,  Test  for  (Blowpipe) 27 

"       "    Qualitative 41 

Coke,  Analysis  of 263 

Colorimetric  Determination  of  Carbon  in  Iron  and  Steel no 

"  "  "Copper 159 

"  "  "  Manganese 200 

"  "  "  Titanium 190 

Combined  Carbon  in  Iron  and  Steel,  Determination  of no 

"          Water,  Determination  of 120 

Combustion,  Analysis  of  Coal  and  Coke 267 

Comparison  of  Scorification  and  Crucible  Assay 396 

"          "  Wet  and  Fire  Assays  for  Gold 399 

Concentrates,  Sampling  of 20 

Concentration  of  Ore,  Tests  for 417 

Constituents  of  Water,  Grouping  of  the. 281 

Copper  ( Precipitant) 83 

"     ,  Determination  of 154 

"        Ingots,  Sampling  of 14 

"        Matte  Blast-furnace  Charges,  The  Calculation  of 428 

"  ",  Special  Method  for  the  Assay  of 250 

"        Analysis  of  Refined 412 

"        Slags,  Analysis  of 307 

"        The  Battery  Assay  for 157 

"      ,     "    Colorimetric  Determination  of 259 

"      ,     "    Volnmetric  Cyanide-assay  for 154 

Iodide          "      "   161 

"      ,  Test  for  (Blowpipe) 27 

"          "      "    (Qualitative) 42 

Corrected  Assay  of  Silver  Sulphides 252 

Crucible-assay  Charges,  Table  of 129 

Crucible  Furnace 55 

Crucibles 59 

Crucible  Assays,  Losses  in 398 

Crushing  and  Pulverizing  of  Ores,  etc 49 

Cupellation 128 

"         ,  Loss  of  Gold  and  Silver  in. 388 

of  Base   Bullion 232 

Cupels 61 

Cuprous  Chloride  (Reagent) 272 

Cyanide  of  Potassium  (Flux) 68 

"       "          "         (Solvent) 70 

"      Process  Tests 401 

D 

Determination  of  Alkalies 227 

"  "        "       in  Water 276 


INDEX.  449 


Determination  of  Aluminium 181 

"  "Ammonia  in  Water 278 

"  "Antimony 147 

"  Arsenic 144 

"  "Barium 224 

"  "Bismuth 163 

"  "Cadmium 165 

"  "Calcium 215 

"  "  Carbon 106 

'«  "  Carbonic  Acid 116 

"  "  Chlorine  in  Water 277 

"  "Chromium 188 

"  "Cobalt 211 

"  "Copper 154 

"  "  Fixed  Carbon  in  Coal  and  Coke 264 

"  "  Fluorine  in  Natural  Phosphates 305 

«'  "  Gold  and  Silver 122 

««  "  "  "  "  in  Base  Bullion 232 

««  "  "  "  "  "  Copper  Matte 250 

««  "  "  ««  "  "  Gold  Bullion 246 

««  "  "  "  "  "  Ores,  Slags,  etc 122 

"  "  "  "  "  "  Silver  Bullion 236 

"  "  "  "  "  "  Silver  Sulphides 252 

"Iron 168 

41  "Lead 136 

"  "  Magnesia  220 

."  "Manganese 194 

"  "  Mercury 133 

•'  "Moisture 119 

"  "Nickel 211 

"  "  Nitrates  in  Water 280 

««  "  Organic  Matter  in  Water 277 

•'  "  "  and  Volatile  Matter  in  Water 274 

«'  "  Platinum 3iia 

«'  "  Potassium 227 

"  "  Phosphorus , 100 

"  "  Pyrites  and  Gypsum  in  Coal  and  Coke 265 

"  "Selenium 414 

"  "  Silica  and  Silicon 77 

"  "Sodium 227 

"  "  Specific  Gravities 293 

"  "  Specific  Gravity  of  Coal  and  Coke 266 

"  "Sulphur 88 

'•  "  Sulphuric  Acid  in  Water 277 

"  "  the  Heating  Power  of  Coal  and  Coke 266 


450  INDEX. 

PAGE 

Determination  of  Tellurium 414 

"Tin 151 

"Titanium igo 

"  "  Total  Solids  in  Water 274 

"  "  Volatile  Matter  in  Coal 263 

"Water , u9 

"Zinc 205 

Drown  on  the  Determination  of  Phosphorus  in  Iron  and  Steel 103 

Drown's  Method  for  the  Separation  of  Iron  and  Alumina 185 

E 

Eggerz's  Method  for  the  Determination  of  Combined  Carbon  in  Iron  and 

Steel no 

Eggerz's  Method  for  the  Determination  of  Graphite  in  Iron  and  Steel 109 

Eggerz's  Mixture  for  Carbon  Standards 114 

Electrolytic  Determination  of  Copper. 157 

"  Iron :87 

"  "  Nickel  and  Cobalt 213 

"          Precipitation  of  Various  Metals,  Table  showing  the 358 

"          Separation  of  Iron  and  Alumina 185 

Elementary  Analysis  of  Coal  and  Coke 267 

Elliott's  Apparatus  for  the  Rapid  Analysis  of  Gases 270 

"        Method  for  the  Determination  of  Total  Carbon 106 

"         "     "  Volumetric  Determination  of  Sulphur 97 

Emmerton's  Method  for  the  Volumetric  Determination  of  Phosphorus 100 

Equation,  The  Writing  of  Chemical 312 

Examination  of  Ores  and  Metallurgical  Products  Preliminary  to  Assaying.     21 
Extraction  of  Gold,  Determination  of  the  Percentage  of  the 404 

F 

Fahlberg-Iles  Method  for  the  Determination  of  Sulphur 88 

Factors,  Calculation  of 323 

"        for  the  Calculation  of  Results,  Table  of 357 

Filtration 61 

Filter-paper 62-87 

Filter-pump B 62 

Fire-assay  for  Gold  and  Silver  Ores  (Crucible) 126 

"       "         "         "     (Scorincation) 123 

"  Platinum 31 1<? 

"  the  Determination  of  Bismuth 164 

"     "                "               "Lead 137 

"    "                "              "Sulphur 91 

"            "    "                "              "  Tin 152 


INDEX. 


451 


PAGE 

Fire-assay  of  Silver  Bullion 238 

Fire-assaying,  Fluxes  used  in 67 

Fixed  Carbon  in  Coal  and  Coke,  Determination  of t . .  264 

Flasks 63 

Flue-dust,  Sampling  of 20 

Fluorine  in  Natural  Phosphates,  Determination  of 305 

4 '      ,  Test  for 28 

Fluxes  used  in  Fire-assaying 67 

"       "       "  Wet  Assaying 66 

Ford's  Method  for  the  Determination  of  Manganese 194 

Formulae,  Calculation  of = 324 

for  the  Calculation  of  Lead  Blast-furnace  Charges 342 

"    "    Conversion  of  Degrees  Baume  into  Specific  Gravity 296 

Free  Ammonia  in  Water,  Determination  of 279 

Funnels 61 

Furnaces 54 

Fused  Ore,  Determination  of  Alumina  in 184 

"                  "              "  Calcium  in 218 

"         "                   "              "  Iron  in 180 

"              "  Manganese  in 204 

"              "  Silica  in 84 

"             "Sulphurin 88 

"              "  Zinc  in...                                                                  .  210 


Gas  Analysis,  Calculation  of  the  Results  of 332 

Gases,  Analysis  of 269 

"    ,  Determination  of  the  Specific  Gravity  of 296 

"    ,  The  Density  and  Weight  of  One  Litre  of  Various 356 

Gay-Lussac's  Method  for  the  Assay  of  Silver  Bullion 240 

Gold  Bullion,  Assay  of ,  ...  246 

"      ,  Effect  of  Impurities  in 373 

"      ,  Loss  in  the  Assay  of 400 

"      ,  Melting  and  Refining  of 371 

"      ,  Sampling  of 380 

"  ,  Determination  of 122 

",  in  Base  Bullion.. „ 233 

"    '  *  Copper  Mattes 250 

"    "Ores ; 122 

""  Silver  Bullion 240 

"  ,  Loss  in  the  Fire-assay  for 386 

"      Ores,  Amalgamation-assay  of 260 

"         "   ,  Mechanical  Assay  of 417 

"         "   ,  Chlorination     "      " 256 

"         "      containing  Metallic  Scales,  Assay  of 258 


452  INDEX. 

PAGF 

Gold,  The  Preparation  of  Pure 382 

Graphite  in  Iron  and  Steel,  Determination  of 109 

Grouping  of  the  Constituents  of  Water 281 

Gypsum  in  Coal  and  Coke,  Determination  of 265 

H 

Hand  Sampling 6 

Handy's  Method  for  the  Volumetric  Determination  of  Phosphorus 103 

Heating  Apparatus 57 

' '  Power  of  Coal  Coke,  Determination  of r  . . .  266 

Hunt's  Remarks  on  the  Colorimetric  Determination  of  Manganese 201 

Hunt's  Remarks  on  the  Determination  of  Combined  Carbon  in  Iron  and 

Steel 113 

Hydrates  of  Potassium  and  Sodium  (Fluxes) 67 

"  "  "  "  "  (Precipitants) 72 

Hydric  Sulphide  (Precipitant) 72 

"  (Reducing  Reagent) 74 

Hydrochloric  Acid  (Solvent) 69 

Hydrodisodic  Phosphate  ( Precipitant) 70 

Hydrofluoric  Acid  (Reagent) 67 

Hydrogen  Peroxide  (Oxidizing  Reagent) 75 

Hyposulphite  of  Sodium  (Solvent) 70 

I 

lies'  Method  for  the  Determination  of  Sulphur. 88 

Impurities  in  Gold  Bullion 373 

Indicators 75 

"         used  in  Acidimetry  and  Alkalimetry 285 

Indirect  Analyses,  Calculation  of  the  Results  of 331 

Iodine,  Test  for  (Blowpipe) 28 

Iron  (Flux) 69 

"   and  Alumina  in  Water,  Determination  of 275 

"  ,  Determination  of 168 

"  ,  Electrolytic  Determination  of , 187 

"     in  Arsenical  and  Antimonial  Ores  and  Mattes,  Determination  of 180 

"     "  Clays,  Determination  of 177 

"     "  Commercial  Alumiinum,  Determination  of 299 

"     "  Fused  Ores,  Determination  of 180 

"     "  Iron  Ores,  Determination  of 176 

"     "  Lead  and  Copper  Ores,  Determination  of 178 

"     "  Limestone,  Determination  of 177 

"     "  Manganese  Ores,  Determination  of 177 

"     *    Mattes,  Determination  of 177 


INDEX. 


453 


CAGE 

Iron,  in  Natural  Phosphates,  Determination  of 304 

"     "  Pig-iron,  Steel,  etc.,              "              " 180 

"     "  Refined  Copper,                                      "... 412 

"     "  Silver  and  Gold  Ores,             "             " 178 

"     "  Slags,  Determination  of 178 

"     "  Sulphides,  Determination  of 177 

"     "  Titaniferous  Ores,  Determination  of 193 

"     Ores,  Determination  of  Alumina  in 183 

"         "                 "               "  Chromium  in 188 

"         "                 "               "  Iron  in 176 

"              "     "     "Titaniferous 193 

"         "                 "               "  Phosphorus  in 100 

"Silicain 77 

Iron  Ores,  Determination  of  Silica  in  Titaniferous 192 

"        "                  "              "  Sulphur  in 88 

"  ,  Sampling  of  Pig- 14 

"  ,  Test  for  (Blowpipe) 29 

"        "      "   (Qualitative) 42 

J 

Jig,  The  Vezin  Laboratory 421 

Johnson's  Method  for  the  Writing  of  Chemical  Equations 316 

K 
Knight's  Method  for  the  Volumetric  Determination  of  Lead 139 

L 

Lead  (Flux) *g  (, 

"    (Precipitant) 73 

"  ,  Comparison  of  Methods  for  the  Determination  of 136 

"  ,  Determination  of 136 

"                                "  by  Fire-assay 137 

"    Flux 68 

"    Gravimetric  Determination  of  (as  Sulphate) 137 

"             "                        "              "  (as  Metallic  Lead) 139 

"    in  Refined  Copper,  Determination  of 412 

"    Ores,  Determination  of  Alumina  in , 184 

"         "                "              "  Calcium  in 217 

"         "                 "              "  Iron  in 178- 

•*.       "                 "              "  Magnesia  in 223: 

««         •«                 "              "  Manganese  in ig& 

"                 "               "Silicain 79. 

"                «•             "Sulphurin 90 


454  INDEX. 

PAGE 

Lead  Slags,  Analysis  of 3°7 

"  ,  Test  for  (Blowpipe) 30 

"       "      "    (Qualitative) 42 

Lead,  The  Volumetric  Determination  with  Potassium  Ferrocyanide  Solution 

of ...139 

Lead,  The  Volumetric  Determination  with  Potassium  Permanganate  Solu- 
tion of. l...    139 

Lead,  The  Volumetric  Determination  with  Molybdate  Solution  of 142 

Lime,  see  Calcium. 

Limestone,  Determination  of  Alumina  in 184 

"'  "  "  Calcium   in 215 

"  "  "  Iron  in . 177 

"  '*  "  Magnesia  in 223 

"  "  "  Silica  in 84 

Litharge  (Flux) 67 

"     ,  Assay  of 128 

Lithium,  Test  for  (Blowpipe) , 30 

"          "       "  (Qualitative) 43 

Losses  of  Gold  and  Silver  in  Fire-assaying 386 

Low's  Apparatus  for  the  Electrolytic  Determination  of  Copper 159 

"     Method  for  the  Determination  of  Copper 154 

"     ft  "  "Manganese 204 

M 

Magnesia,  Determination  of 220 

"          in  Clays,  Determination  of 223 

"Limestone                      " 223 

"  Natural  Phosphates,  Determination  of 304 

"  Ores,  Determination  of 223 

"           "Slags,            "              "   221 

"           "Water,           "              "  275 

"          Mixture  (Precipitant) . .  • 71 

Magnesium,  Test  for  (Blowpipe) 31 

"      "  (Qualitative) 43 

Manganese,  Determination  of 194 

"           by  Ford's  Method,  Determination  of „ 194 

"           "   Low's  Method,              "             " 204 

"    Volhard's  Method,        "              " 198 

"           "Williams'        "              "              " 196 

in  Ores,  Determination  of 198 

"   Iron  and  Steel,  Determination  of 194 

"  Slags,  Determination  of 204 

"           Ores,  Determination  of  Alumina  in 184 

"              "                  "              "Ironin 177 


INDEX.  455 

PAGE 

Manganese  Ores,  Determination  of  Silica  in 77 

•   "         ,  Test  for  (Blowpipe) ....  31 

"      "  (Qualitative) ,43 

Marguerite's  Method  for  the  Volumetric  Determination  of  Iron 169 

Mattes,  Determination  of  Alumina  in 184 

'*                     "              "  Iron  in 177 

"              "  Silica  in 84 

Measures  and  Weights,  Table  of 353 

Mechanical  Assay  of  Ores 417 

Melting  and  Refining  Gold  Bullion 371 

Mercury,  Determination  of 133 

'*      ,  Test  for  (Blowpipe) 32 

"            "        "  (Qualitative) 43 

Metallurgical  Products,  Sampling  of 14 

Metals,  The  Characteristic  Properties  of 359 

"         "    Electrolytic  Precipitation  of 358 

Moisture,  Determination  of . . , 119 

"          in  Coal  and  Coke,  Determination  of 263 

"          "  Natural  Phosphates,       "           " 300 

Moly bdate  Solution  ( Precipitant) 71 

Molybdenum,  Test  for  (Blowpipe) 32 

"                "      ''(Qualitative) 43 

Moulds  used  in  Assaying 50 

Moses,  List  of  Blowpipe  Tests  by  Prof.  A.  J 22 

Muffle  Furnace  for  Coke  and  Charcoal 57 

"   SoftCoal 56 

N 

Nickel,  Determination  of % 21 1 

"    ,  Test  for  (Blowpipe) 32 

"           "      "(Qualitative) 43 

Nitrate  of  Ammonium  (Oxidizing  Reagent) 75 

"        "  Silver  (Precipitant) 71 

"  Soda  (Flux) 67 

"        "  Soda  (Oxidizing  Reagent) 75 

Nitrates  in  Water,  Determination  of 280 

Nitre  (Flux) 68 

Nitric  Acid  (Oxidizing  Reagent) 75 

"     (Solvent) 69 

"         "  ,  Test  for  (Blowpipe) 33 

"         "        "       "   (Qualitative) 44 

O 

Operations  and  Apparatus 49 

Ores,  Sampling  of....   , 6 


456 


INDEX. 


Organic  and  Volatile  Matter  in  Water,  Determination  of , 274 

"        Matter  in  Natural  Phosphates,              "              " 301 

Oxalate  of  Ammonium  (Precipitant). .    71 

Oxalic  Acid  (Reagent) 70 

Oxidizing  Reagents 74 

Oxygen  (Oxidizing  Reagent) 74 

"       consumed  by  Organic  Matter  in  Water 277 

* '       in  Refined  Copper,  Determination  of 416 

P 

Pan  for  the  Amalgamation  Assay 262 

Parting  Buttons  from  the  Assay  of  Base  Bullion 233 

"       Gold  and  Silver  Buttons 131 

"          "     Bullion 246 

Pearce's  Method  for  the  Determination  of  Arsenic 144 

Peeny's  Method  for  the  Volumetric  Determination  of  Iron 173 

Percentage,  Calculation  of .  . ,  321 

"            of  Extraction ,  Determination  of 404 

Permanganate  of  Potassium  (Precipitant) 71 

"             "           "          (Oxidizing  Reagent) „ 75 

"             "  Test  for  Organic  Matter  in  Water 277 

Peroxide  of  Hydrogen  (Oxidizing  Reagent) 75 

Phosphate,  Hydrodisodic  (Precipitant) 70 

Phosphates,  Analysis  of  Natural 300 

Phosphoric  Acid  in  Natural  Phosphates,  Determination  of 301 

Phosphorus,  Determination  of 100 

11          ,  Test  for  (Blowpipe) 33 

"               •*      "  (Qualitative) 44 

Pig-iron,  Determination  of  Chromium  in 189 

"       "                                  "  Combined  Carbon  in no 

"       "                                  "Graphite  in 109 

"       "                  "              "  Iron  in 180 

41       "                  "              "  Phosphorus  in 100 

"       "                  "              "  Silicon  in 85 

«'       "                  "              "  Sulphur  in 94 

"       "                  "              "  Total  Carbon  in 106 

Pipettes 63 

Platinum  Crucibles 60 

"       ,  Determination  of,  in  Ores  and  Alloys 31 1« 

Porcelain  Crucibles 60 

Potash,  Analysis  of  Commercial 287 

Potassium  and  Sodium,  Direct  Determination  of 229 

•'     .Indirect             "              " 228 

"        ,  Determination  of , 227 


INDEX.  457 

PAGE 

Potassium  Bichromate  (Reagent) „ 75 

Bisulphate  (Flux) 66 

Carbonate  (Flux) 66 

*•          Chlorate  (Oxidizing  Reagent) 75 

"          Cyanide  (Flux) 68 

"                "        (Solvent) 70 

Hydrate  (Flux) 67 

"                 "         (Precipitant)..- 72 

"                 "         (Reagent  in  Gas  Analysis)...  i 272 

"          Permanganate  (Oxidizing  Reagent) 75 

"                      "              (Precipitant) = 71 

"          Pyrogallate  (Reagent  in  Gas  Analysis) 272 

"        ,  Test  for  (Blowpipe) 33 

"              "       "  (Qualitative) 45 

Precipitants 70 

Precipitates,  Table  showing  the  Properties  of 360 

Preliminary  Assay  of  Silver  Bullion 237 

"           Examination  of  Ores  and  Metallurgical  Products 21 

Preparation  of  Pure  Gold  and  Silver 382 

Proof  in  the  Assay  of  Silver  Bullion 238 

Properties  of  Metals,  Table  of  the 359 

Pulverizing 49 

Pyrites  in  Coal  and  Coke,  Determination  of 265 

Q 

Qualitative  Tests 38 

R 

Reagents 66 

' '         used  in  the  Rapid  Analysis  of  Gases , . .  272 

Reed  on  Ore  Sampling I4 

Refined  Copper,  Analysis  of 412 

Refining  Gold  Bullion 374 

Richards  Sorting-tube 424 

Rolls 51 

Rose  Crucible 60 

Rose's  Method  for  the  Determination  of  Bismuth 16? 

"        "     "  "  "   Tin 151 

S 

Salt  (Flux) 68 

4 '  Solution  in  the  Volumetric  Assay  for  Silver 240 

Sampling  by  Hand  (Ores) 6 

"      ,  Combined  Hand  and  Mechanical  (Ores). 7 


458 


INDEX. 


PAGE 

Sampling,  Mechanical  (Ores).. 10 

"         of  Base  Bullion „ 14 

"         "  Copper  Ingots 14 

"         "  Concentrates 20 

"         "  Flue-dust 20 

"         "  Gold  Bullion 380 

"         "  Pig-iron  and  Steel 14 

"  Mattes 20 

"        "  Silver  Bullion 18 

"  Silver  Sulphides 20 

"  Slags 18 

"        "  Tailings 20 

Scorincation 125 

Assay  Charges,  Table  of 124 

Assay  for  Gold  and  Silver : 123 

"         ,  Loss  of  Gold  and  Silver  in 393 

Scorifiers  61 

Selenium  in  Refined  Copper. .  .  e 414 

"       ,  Test  for  (Blowpipe) 34 

"  "     "     (Qualitative) 45 

Silica  (Flux) •  68 

"    ,    Determination  of 77 

"     in  Clays,  Determination  of 84 

"      "  Copper  Furnace  Slags,  Determination  of 84 

"      "  Iron  Furnace  Slags,  Determination  of 83 

"      "  Iron  Ores,  Determination  of 77 

'*      "  Lead  Ores,  Determination  cf 79 

"      "  Limestone,  Determination  of 84 

"      "  Mattes,  Determination  of 84 

"      "  Natural  Phosphates,  Determination  of 301 

"      "  Silver  and  Gold  Ores,  Determination  of. 79 

"      "  Slags  (Lead),  Determination  of , 80 

"      "  Titaniferous  Ores,  Determination  of 87 

"      ,  Test  for  the  Purity  of 86 

Silicon  in  Iron  and  Steel,  Determination  of 85 

"       "  Commercial  Aluminium,  Determination  of 298 

"     ,  Test  for  (Blowpipe) ; 34 

"        "        "     (Qualitative) 45 

Silver  Bullion  Assay 236 

"     ,  Sampling  of 18 

Chloride  in  Ores,  Determination  of 254 

"      Crucibles 60 

"  ,  Crucible  Assay  for...    126 

"  ,  Determination  of 122 

in  Base  Bullion,  Determination  of.. .  ,    232 


INDEX.  459 

PAGE 

Silver  in  Copper  Mattes,  Determination  of 250 

"      "  Ores,  Determination  of 122 

"      "  Slags,  Determination  of 129 

"    ,    Loss  in  the  Fire-assay  for 386 

"      Nitrate  (Precipitant) 7I 

"      Ores,  Amalgamation  Assay  of 261 

**         "    ,  Chlorination  Assay  of 254 

"         "     containing  Metallic  Scales,  Assay  of 258 

"         "   ,  Determination  of  Alumina  in 184 

"  Calcium  in 217 

"Ironin ; I?8 

"  Magnesia  in 223 

"  Manganese 198 

"Silicain , 79 

'    ,  Mechanical  Assay  of 417 

"  ,  Scorification  Assay  for 123 

i(      Sulphides,  Sampling  of 20 

"       ,  Assay  of 252 

"      Sulphides,  Loss  of  Silver  in  the  Assay  of 394 

"      Sulphate  in  Ores,  Determination   of 255 

"  ,  Preparation  of  Pure 384 

"  ,  Test  for  (Blowpipe) 34 

"     "    (Qualitative) 45 

Slags    Analysis  of 307 

"  .  Sampling  of 18 

"      for  Lead  Smelting,  Table  of  Type 338 

Sr»»Mi's  (J.  L.)  Method  for  the  Determination  of  Alkalies 230 

Sodium  Acetate  (Precipitant) 72 

"       and  Potassium,  Direct  Determination  of 229 

"         ,  Indirect  Determination  of „ 228 

Bicarbonate  (Flux) 67 

Carbonate  (Flux) 66 

"               "          (Precipitant) >2 

Hydrate  (Flux) 67 

%<               "       (Precipitant) 72 

l*       Hyposulphite  (Solvent) 70 

"'        Nitrate  (Oxidizing  Reagent) 75 

(Flux) 67 

"        Sulphide  (Precipitant) v  72 

"        Sulphite  (Reducing  Reagent) 74 

"     ,  Test  for  (Blowpipe) 35 

"           "      "    (Qualitative) 46 

Solid  Matter  in  Water,  Determination  of 274 

Solvents 69 

Specific  Gravity  and  Weight  of  Gases,  Table  of  the 356 

"             "       Determinations 293 


460  INDEX. 

PAGE 

Specific  Gravity  of  Coal  and  Coke,  Determination  of 266 

"        "  Liquids  and  Corresponding  Degrees  Beaum£ 297 

Split  Shovel 9 

Standard  Acid  Solutions 282 

"       Alkali  Solutions 285 

Stannous  Chloride  (Reducing  Reagent) 74 

Steel,  Determination  of  Combined  Carbon  in no 

"                   "             "  Chromium  in 189 

"                   "             "  Graphite  in  109 

"                    •'             "  Iron  in 180 

•«                   "             "  Phosphorus  in 100 

"Siliconin 85 

'•             "  Sulphur  in 94 

"                  "             "  Total  Carbon  in 106 

Stoichiometry 321 

Strontium,  Test  for  (Blowpipe) 35 

'*             "     "    (Qualitative) 46 

Sulphur,  Determination  of 88 

"         in  Refined  Copper,  Determination  of 415 

Sulphate  of  Silver  in  Ores,  Determination  of 255 

Sulphide  of  Ammonium  (Solvent) 70 

"        "             "          (Precipitant 71 

"        "  Sodium  (Reducing  Reagent) 74 

Sulphur  by  Absorption  in  Alkaline  Solution  of  Cadmium  Sulphate,  Deter- 
mination of 96 

Sulphur  by  Absorption  in  Alkaline  Solution  of  Lead  Nitrate,  Determina- 
tion of 99 

Sulphur  by  Fahlberg-Iles  Method,  Determination  of 88 

"       "  Fire-assay,  Determination  of 91 

Sulphur  by  Oxidation  with  Potassium  Chlorate  and  Nitric  Acid,  Determi- 
nation of 90 

Sulphur  by  Volumetric  Method,  Determination  of 92 

Sulphuretted  Hydrogen  (Reducing  Reagent) 74 

(Precipitant) 72 

Sulphuric  Acid  (Precipitant) 72 

(Solvent) 69 

"         "         in  Water,  Determination  of 277 

Sulphur,  Test  for  (Blowpipe) 35 

"          "      "  (Qualitative) 46 

T 

Table  of  Atomic  Weights 354 

"     "  Crucible  Assay  Charges 129 

"     "  Factors 357 


INDEX.  461 

PAGE 

Table  of  Gramme  and  Pound  Equivalents 257 

"     "  Scorification  Assay  Charges 124 

"     "  Specific  Gravities  and  Weight  of  One  Litre  of  Various  Gases 356 

Table    of   the   Specific   Gravities  Corresponding   to   Degrees    Beaum6   of 

Liquids 297 

Table  of  the  Tension  of  Aqueous  Vapor 355 

"     "  Type-lead  Slags 338 

"     "  Volumetric  Determinations 368 

"     "  Weights  and  Measures 353 

Table  of  Weights  of  Lead  and  Silver  to  be  used  in  the  Assay  of  Silver 

Bullion « 238 

Table  showing  the  Characteristic  Properties  of  Various  Metals 359 

"  "    Electrolytic  Precipitation  of  Various  Metals 358 

"  "    Properties  of  Precipitates 360 

Tartaric  Acid  (Reagent) 70 

Tellurium  in  Refined  Copper * 414 

"       ,  Test  for  (Blowpipe) 36 

"  "      "  (Qualitative) 46 

Tension  of  Aqueous  Vapor,  Table  showing  the „ 355 

Test-lead,  Assay  of 124 

Tests,  Blowpipe 22 

"   ,  Qualitative 38 

"      used  in  the  Cyanide  Process 401 

Tin,  Fire-assay  for 152 

"  ,  Determination  of 151 

"  ,  Test  for  (Blowpipe) 36 

"      "(Qualitative) 46 

Titaniferous  Ores,  Determination  of  Chromium  in 189 

"Iron  " 193 

"Silica  " 87-192 

Titanium,  Determination  of 190 

"       ,  Test  for  (Blowpipe) 37 

"  "      "    (Qualitative) 47 

Total  Carbon,  Determination  of 106 

Tungsten,  Test  for  (Blowpipe) .• 37 

"  "      "(Qualitative) 47 

U 

Uranium,  Test  for  (Blowpipe) 37 

"  "      "(Qualitative) 47 

V 

Vanadium,  Test  for  (Blowpipe) 38 

"  "      "(Qualitative) 48 


462  INDEX. 

PAGE 

Vanning  Plaque 422 

Vezin's  Jig 421 

Volatile  Matter  in  Coal  and  Coke,  Determination  of 263 

Volhard's  Method  for  the  Volumetric  Determination  of  Manganese 198 

"  Silver 245 

Volumetric  Assay  of  Silver  Bullion,  Calculation  of  the  Results  of  the 244 

Determination  of  Arsenic 145 

"                                      "Cadmium ; 167 

w  "  "Calcium ,215 

"  Copper  with  Cyanide  Solution 154 

"                     "               "       "        by  the  Iodide  Method 161 

"                      "               "  Lead  with  Molybdate  Solution 142 

"                                       "       '         "     Permanganate   Solution 139 

"                     "               "  Manganese  by  Low's  Method 204 

"  "  "  "          "  Volhard's   Method ....198 

"                     "              "             "          "  Williams'  Method 197 

"  Phosphorus  by  Emmerton's  Method 100 

"  Handy's  Method 103 

"                    "              "  Silver  by  Gay-Lussac's  Method 240 

"                    "              "      "       "   Volhard's  Method 245 

••                     "              "Sulphur 92 

"                    "              "        "      by  Elliott's  Method 97 

"                     "               "Zinc 205 

Determinations,  Table  of 368 

"          Solutions,  Calculations  involved  in  the  Preparation  and  Use  of  328 

Von  Schulz  and  Low's  Method  for  the  Determination  of  Lead 139 

"        "          "        "           "         "      "              "               "Zinc 207 

W 

Waller's  Method  for  the  Writing  of  Chemical  Equations 314 

Water,  Distilled  (Reagent) 69 

"    ,  Analysis  of 274 

"    ,  Determination  of 119 

' '       in  Natural  Phosphates,  Determination  of 30 1 

Weighing 51 

"       Gold  and  Silver  Buttons , 233 

Weights 51 

"        and  Measures,  Table  of 353 

"      ,  Table  of  Atomic 354 

Weller's  Colorimetric  Method  for  the  Determination  of  Titanium 190 

Whitehead's  Method  for  the  Determination  of  Gold  and  Silver  in  Copper 

Matte 250 

White-lead,  Analysis  of 291 

Williams'  Method  for  the  Determination  of  Manganese 196 


INDEX.  463 

PAGE 

Wind  Furnaces 55 

Writing  of  Chemical  Equations 312 

Zinc  (Precipitant)  .. 72 

"  ,  Determination  of. 205 

"     in  Ores  containing  Cadmium,  Determination  of 210 

"     in  Slags,  Determination  of 210 

"  ,Test  for  (Blowpipe) 38 

"      "  (Qualitative) 48 


UNIVERSITY 

CALIFOB 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 
LOAN  DEPT. 

This  book  is  due  on  the  last  date  stamped  below,  or 

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26Jut'58J  Ng 

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R     ~  °  ""' 

JUL  12  1958 

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*tnt\ 

General  Library 
LD  21A-50m-8,'57                                 University  of  California 
(C8481slO)476B                                                Berkeley 

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